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 $59.38   13.748%   $67.5436   $67.54   $67.55   $67.50  
  Purchase #2 $55.68   5.143%   $58.5436   $58.54   $58.55   $58.50  
  Purchase #3 $149.75   12.196%   $168.0135   $168.01   $168.00   $168.00  
  Purchase #4 $108.78   3.403%   $112.4818   $112.48   $112.50   $112.50  
  Purchase #5 $80.39   8.391%   $87.1355   $87.14   $87.15   $87.10  
  Purchase #6 $220.52   10.569%   $243.8268   $243.83   $243.85   $243.80  
  Purchase #7 $153.63   6.385%   $163.4393   $163.44   $163.45   $163.40  
  7 purchase totals = $828.13       $900.9841   $900.98   $901.05   $900.80