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 $51.81   10.499%   $57.2495   $57.25   $57.25   $57.20  
  Purchase #2 $202.39   11.572%   $225.8106   $225.81   $225.80   $225.80  
  Purchase #3 $94.50   7.514%   $101.6007   $101.60   $101.60   $101.60  
  Purchase #4 $219.55   13.755%   $249.7491   $249.75   $249.75   $249.70  
  Purchase #5 $65.72   11.666%   $73.3869   $73.39   $73.40   $73.40  
  Purchase #6 $94.70   11.566%   $105.653   $105.65   $105.65   $105.70  
  Purchase #7 $149.89   9.598%   $164.2764   $164.28   $164.30   $164.30  
  7 purchase totals = $878.56       $977.7262   $977.73   $977.75   $977.70