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 $56.36   3.853%   $58.5316   $58.53   $58.55   $58.50  
  Purchase #2 $209.26   13.581%   $237.6796   $237.68   $237.70   $237.70  
  Purchase #3 $138.61   12.396%   $155.7921   $155.79   $155.80   $155.80  
  Purchase #4 $86.49   5.318%   $91.0895   $91.09   $91.10   $91.10  
  Purchase #5 $206.88   4.824%   $216.8599   $216.86   $216.85   $216.90  
  Purchase #6 $215.84   12.123%   $242.0063   $242.01   $242.00   $242.00  
  Purchase #7 $66.72   4.537%   $69.7471   $69.75   $69.75   $69.70  
  7 purchase totals = $980.16       $1,071.7061   $1,071.71   $1,071.75   $1,071.70