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 $45.68   6.568%   $48.6803   $48.68   $48.70   $48.70  
  Purchase #2 $59.87   11.729%   $66.8922   $66.89   $66.90   $66.90  
  Purchase #3 $91.56   3.124%   $94.4203   $94.42   $94.40   $94.40  
  Purchase #4 $28.48   12.703%   $32.0978   $32.10   $32.10   $32.10  
  Purchase #5 $98.31   3.763%   $102.0094   $102.01   $102.00   $102.00  
  Purchase #6 $227.59   3.763%   $236.1542   $236.15   $236.15   $236.20  
  Purchase #7 $231.29   8.777%   $251.5903   $251.59   $251.60   $251.60  
  7 purchase totals = $782.78       $831.8445   $831.84   $831.85   $831.90