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 $131.63   12.591%   $148.2035   $148.20   $148.20   $148.20  
  Purchase #2 $58.29   11.139%   $64.7829   $64.78   $64.80   $64.80  
  Purchase #3 $116.82   8.637%   $126.9097   $126.91   $126.90   $126.90  
  Purchase #4 $141.27   4.617%   $147.7924   $147.79   $147.80   $147.80  
  Purchase #5 $133.33   13.155%   $150.8696   $150.87   $150.85   $150.90  
  Purchase #6 $227.86   13.376%   $258.3386   $258.34   $258.35   $258.30  
  Purchase #7 $210.62   6.536%   $224.3861   $224.39   $224.40   $224.40  
  7 purchase totals = $1,019.82       $1,121.2828   $1,121.28   $1,121.30   $1,121.30