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 $232.96   13.505%   $264.4212   $264.42   $264.40   $264.40  
  Purchase #2 $230.30   5.324%   $242.5612   $242.56   $242.55   $242.60  
  Purchase #3 $195.91   10.863%   $217.1917   $217.19   $217.20   $217.20  
  Purchase #4 $191.77   8.219%   $207.5316   $207.53   $207.55   $207.50  
  Purchase #5 $141.85   6.156%   $150.5823   $150.58   $150.60   $150.60  
  Purchase #6 $163.42   8.281%   $176.9528   $176.95   $176.95   $177.00  
  Purchase #7 $43.77   6.779%   $46.7372   $46.74   $46.75   $46.70  
  7 purchase totals = $1,199.98       $1,305.9780   $1,305.97   $1,306.00   $1,306.00