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 $185.72   10.492%   $205.2057   $205.21   $205.20   $205.20  
  Purchase #2 $57.70   12.160%   $64.7163   $64.72   $64.70   $64.70  
  Purchase #3 $21.91   13.139%   $24.7888   $24.79   $24.80   $24.80  
  Purchase #4 $187.54   10.361%   $206.971   $206.97   $206.95   $207.00  
  Purchase #5 $77.74   5.407%   $81.9434   $81.94   $81.95   $81.90  
  Purchase #6 $78.52   6.157%   $83.3545   $83.35   $83.35   $83.40  
  Purchase #7 $51.66   9.489%   $56.562   $56.56   $56.55   $56.60  
  7 purchase totals = $660.79       $723.5417   $723.54   $723.50   $723.60