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 $134.88   5.133%   $141.8034   $141.80   $141.80   $141.80  
  Purchase #2 $216.53   5.560%   $228.5691   $228.57   $228.55   $228.60  
  Purchase #3 $119.39   5.313%   $125.7332   $125.73   $125.75   $125.70  
  Purchase #4 $163.27   11.637%   $182.2697   $182.27   $182.25   $182.30  
  Purchase #5 $69.27   6.446%   $73.7351   $73.74   $73.75   $73.70  
  Purchase #6 $43.52   7.294%   $46.6943   $46.69   $46.70   $46.70  
  Purchase #7 $112.38   9.795%   $123.3876   $123.39   $123.40   $123.40  
  7 purchase totals = $859.24       $922.1924   $922.19   $922.20   $922.20