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 $83.73   9.474%   $91.6626   $91.66   $91.65   $91.70  
  Purchase #2 $187.89   12.105%   $210.6341   $210.63   $210.65   $210.60  
  Purchase #3 $29.56   8.505%   $32.0741   $32.07   $32.05   $32.10  
  Purchase #4 $227.29   6.787%   $242.7162   $242.72   $242.70   $242.70  
  Purchase #5 $6.77   12.344%   $7.6057   $7.61   $7.60   $7.60  
  Purchase #6 $230.52   7.110%   $246.91   $246.91   $246.90   $246.90  
  Purchase #7 $180.27   8.347%   $195.3171   $195.32   $195.30   $195.30  
  7 purchase totals = $946.03       $1,026.9198   $1,026.92   $1,026.85   $1,026.90