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 $94.87   7.761%   $102.2329   $102.23   $102.25   $102.20  
  Purchase #2 $185.97   11.824%   $207.9591   $207.96   $207.95   $208.00  
  Purchase #3 $219.34   12.370%   $246.4724   $246.47   $246.45   $246.50  
  Purchase #4 $13.52   11.406%   $15.0621   $15.06   $15.05   $15.10  
  Purchase #5 $64.37   9.681%   $70.6017   $70.60   $70.60   $70.60  
  Purchase #6 $138.33   7.336%   $148.4779   $148.48   $148.50   $148.50  
  Purchase #7 $164.41   12.776%   $185.415   $185.42   $185.40   $185.40  
  7 purchase totals = $880.81       $976.2211   $976.22   $976.20   $976.30