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 $30.61   5.526%   $32.3015   $32.30   $32.30   $32.30  
  Purchase #2 $6.72   7.284%   $7.2095   $7.21   $7.20   $7.20  
  Purchase #3 $207.63   7.394%   $222.9822   $222.98   $223.00   $223.00  
  Purchase #4 $170.79   11.633%   $190.658   $190.66   $190.65   $190.70  
  Purchase #5 $61.39   5.484%   $64.7566   $64.76   $64.75   $64.80  
  Purchase #6 $247.97   11.179%   $275.6906   $275.69   $275.70   $275.70  
  Purchase #7 $40.91   5.816%   $43.2893   $43.29   $43.30   $43.30  
  7 purchase totals = $766.02       $836.8877   $836.89   $836.90   $837.00