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 $94.82   8.774%   $103.1395   $103.14   $103.15   $103.10  
  Purchase #2 $82.35   5.242%   $86.6668   $86.67   $86.65   $86.70  
  Purchase #3 $29.90   7.840%   $32.2442   $32.24   $32.25   $32.20  
  Purchase #4 $27.61   8.601%   $29.9847   $29.98   $30.00   $30.00  
  Purchase #5 $183.41   11.519%   $204.537   $204.54   $204.55   $204.50  
  Purchase #6 $140.52   8.779%   $152.8563   $152.86   $152.85   $152.90  
  Purchase #7 $139.82   3.341%   $144.4914   $144.49   $144.50   $144.50  
  7 purchase totals = $698.43       $753.9199   $753.92   $753.95   $753.90