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 $56.46   11.854%   $63.1528   $63.15   $63.15   $63.20  
  Purchase #2 $219.72   11.563%   $245.1262   $245.13   $245.15   $245.10  
  Purchase #3 $200.93   8.872%   $218.7565   $218.76   $218.75   $218.80  
  Purchase #4 $91.73   5.618%   $96.8834   $96.88   $96.90   $96.90  
  Purchase #5 $250.60   13.867%   $285.3507   $285.35   $285.35   $285.40  
  Purchase #6 $56.68   9.795%   $62.2318   $62.23   $62.25   $62.20  
  Purchase #7 $211.66   7.316%   $227.145   $227.15   $227.15   $227.10  
  7 purchase totals = $1,087.78       $1,198.6464   $1,198.65   $1,198.70   $1,198.70