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 $48.46   4.552%   $50.6659   $50.67   $50.65   $50.70  
  Purchase #2 $181.74   4.111%   $189.2113   $189.21   $189.20   $189.20  
  Purchase #3 $219.84   10.268%   $242.4132   $242.41   $242.40   $242.40  
  Purchase #4 $69.85   8.822%   $76.0122   $76.01   $76.00   $76.00  
  Purchase #5 $99.41   6.139%   $105.5128   $105.51   $105.50   $105.50  
  Purchase #6 $225.71   10.337%   $249.0416   $249.04   $249.05   $249.00  
  Purchase #7 $43.57   6.239%   $46.2883   $46.29   $46.30   $46.30  
  7 purchase totals = $888.58       $959.1453   $959.14   $959.10   $959.10