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 $222.35   11.507%   $247.9358   $247.94   $247.95   $247.90  
  Purchase #2 $145.44   5.164%   $152.9505   $152.95   $152.95   $153.00  
  Purchase #3 $27.63   5.387%   $29.1184   $29.12   $29.10   $29.10  
  Purchase #4 $57.59   13.483%   $65.3549   $65.35   $65.35   $65.40  
  Purchase #5 $201.48   11.200%   $224.0458   $224.05   $224.05   $224.00  
  Purchase #6 $121.39   3.568%   $125.7212   $125.72   $125.70   $125.70  
  Purchase #7 $159.43   5.823%   $168.7136   $168.71   $168.70   $168.70  
  7 purchase totals = $935.31       $1,013.8402   $1,013.84   $1,013.80   $1,013.80