Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $194.67   5.576%   $205.5248   $205.52   $205.50   $205.50  
  Purchase #2 $128.99   5.299%   $135.8252   $135.83   $135.85   $135.80  
  Purchase #3 $146.70   6.499%   $156.234   $156.23   $156.25   $156.20  
  Purchase #4 $181.79   12.432%   $204.3901   $204.39   $204.40   $204.40  
  Purchase #5 $209.34   13.628%   $237.8689   $237.87   $237.85   $237.90  
  Purchase #6 $227.75   12.117%   $255.3465   $255.35   $255.35   $255.30  
  Purchase #7 $211.66   8.377%   $229.3908   $229.39   $229.40   $229.40  
  7 purchase totals = $1,300.90       $1,424.5803   $1,424.58   $1,424.60   $1,424.50