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 $34.31   4.512%   $35.8581   $35.86   $35.85   $35.90  
  Purchase #2 $244.94   9.401%   $267.9668   $267.97   $267.95   $268.00  
  Purchase #3 $234.57   12.697%   $264.3534   $264.35   $264.35   $264.40  
  Purchase #4 $58.63   5.866%   $62.0692   $62.07   $62.05   $62.10  
  Purchase #5 $137.70   6.731%   $146.9686   $146.97   $146.95   $147.00  
  Purchase #6 $149.74   4.384%   $156.3046   $156.30   $156.30   $156.30  
  Purchase #7 $206.76   5.306%   $217.7307   $217.73   $217.75   $217.70  
  7 purchase totals = $1,066.65       $1,151.2514   $1,151.25   $1,151.20   $1,151.40