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 $69.46   5.816%   $73.4998   $73.50   $73.50   $73.50  
  Purchase #2 $153.31   3.848%   $159.2094   $159.21   $159.20   $159.20  
  Purchase #3 $71.82   12.711%   $80.949   $80.95   $80.95   $80.90  
  Purchase #4 $70.35   10.823%   $77.964   $77.96   $77.95   $78.00  
  Purchase #5 $161.50   11.716%   $180.4213   $180.42   $180.40   $180.40  
  Purchase #6 $221.43   10.450%   $244.5694   $244.57   $244.55   $244.60  
  Purchase #7 $106.48   12.192%   $119.462   $119.46   $119.45   $119.50  
  7 purchase totals = $854.35       $936.0749   $936.07   $936.00   $936.10