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 $141.83   13.670%   $161.2182   $161.22   $161.20   $161.20  
  Purchase #2 $171.53   6.664%   $182.9608   $182.96   $182.95   $183.00  
  Purchase #3 $233.82   5.457%   $246.5796   $246.58   $246.60   $246.60  
  Purchase #4 $244.40   8.519%   $265.2204   $265.22   $265.20   $265.20  
  Purchase #5 $195.45   6.181%   $207.5308   $207.53   $207.55   $207.50  
  Purchase #6 $138.89   3.330%   $143.515   $143.52   $143.50   $143.50  
  Purchase #7 $129.76   4.440%   $135.5213   $135.52   $135.50   $135.50  
  7 purchase totals = $1,255.68       $1,342.5461   $1,342.55   $1,342.50   $1,342.50