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 $14.31   13.541%   $16.2477   $16.25   $16.25   $16.20  
  Purchase #2 $222.86   9.194%   $243.3497   $243.35   $243.35   $243.30  
  Purchase #3 $60.68   13.379%   $68.7984   $68.80   $68.80   $68.80  
  Purchase #4 $15.38   8.401%   $16.6721   $16.67   $16.65   $16.70  
  Purchase #5 $116.25   13.493%   $131.9356   $131.94   $131.95   $131.90  
  Purchase #6 $202.98   12.250%   $227.8451   $227.85   $227.85   $227.80  
  Purchase #7 $229.97   8.275%   $249   $249.00   $249.00   $249.00  
  7 purchase totals = $862.43       $953.8486   $953.86   $953.85   $953.70