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 $65.37   4.832%   $68.5287   $68.53   $68.55   $68.50  
  Purchase #2 $185.34   5.174%   $194.9295   $194.93   $194.95   $194.90  
  Purchase #3 $219.88   8.151%   $237.8024   $237.80   $237.80   $237.80  
  Purchase #4 $246.67   9.677%   $270.5403   $270.54   $270.55   $270.50  
  Purchase #5 $6.33   11.305%   $7.0456   $7.05   $7.05   $7.00  
  Purchase #6 $115.93   13.199%   $131.2316   $131.23   $131.25   $131.20  
  Purchase #7 $94.62   12.492%   $106.4399   $106.44   $106.45   $106.40  
  7 purchase totals = $934.14       $1,016.5180   $1,016.52   $1,016.60   $1,016.30