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 $179.26   8.209%   $193.9755   $193.98   $194.00   $194.00  
  Purchase #2 $88.93   12.635%   $100.1663   $100.17   $100.15   $100.20  
  Purchase #3 $101.65   13.520%   $115.3931   $115.39   $115.40   $115.40  
  Purchase #4 $236.28   9.171%   $257.9492   $257.95   $257.95   $257.90  
  Purchase #5 $179.42   4.457%   $187.4167   $187.42   $187.40   $187.40  
  Purchase #6 $188.85   3.668%   $195.777   $195.78   $195.80   $195.80  
  Purchase #7 $40.92   7.352%   $43.9284   $43.93   $43.95   $43.90  
  7 purchase totals = $1,015.31       $1,094.6062   $1,094.62   $1,094.65   $1,094.60