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 $48.95   3.653%   $50.7381   $50.74   $50.75   $50.70  
  Purchase #2 $242.54   6.192%   $257.5581   $257.56   $257.55   $257.60  
  Purchase #3 $29.95   3.350%   $30.9533   $30.95   $30.95   $31.00  
  Purchase #4 $147.48   8.317%   $159.7459   $159.75   $159.75   $159.70  
  Purchase #5 $244.51   3.471%   $252.9969   $253.00   $253.00   $253.00  
  Purchase #6 $90.77   10.540%   $100.3372   $100.34   $100.35   $100.30  
  Purchase #7 $182.47   3.612%   $189.0608   $189.06   $189.05   $189.10  
  7 purchase totals = $986.67       $1,041.3903   $1,041.40   $1,041.40   $1,041.40