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 $72.37   4.435%   $75.5796   $75.58   $75.60   $75.60  
  Purchase #2 $227.75   11.267%   $253.4106   $253.41   $253.40   $253.40  
  Purchase #3 $118.35   12.618%   $133.2834   $133.28   $133.30   $133.30  
  Purchase #4 $204.30   8.486%   $221.6369   $221.64   $221.65   $221.60  
  Purchase #5 $133.56   12.365%   $150.0747   $150.07   $150.05   $150.10  
  Purchase #6 $146.85   5.803%   $155.3717   $155.37   $155.35   $155.40  
  Purchase #7 $11.96   13.594%   $13.5858   $13.59   $13.60   $13.60  
  7 purchase totals = $915.14       $1,002.9427   $1,002.94   $1,002.95   $1,003.00