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 $49.26   13.729%   $56.0229   $56.02   $56.00   $56.00  
  Purchase #2 $218.40   12.615%   $245.9512   $245.95   $245.95   $246.00  
  Purchase #3 $94.43   13.533%   $107.2092   $107.21   $107.20   $107.20  
  Purchase #4 $230.46   11.228%   $256.336   $256.34   $256.35   $256.30  
  Purchase #5 $54.53   10.857%   $60.4503   $60.45   $60.45   $60.50  
  Purchase #6 $170.28   7.366%   $182.8228   $182.82   $182.80   $182.80  
  Purchase #7 $114.71   5.433%   $120.9422   $120.94   $120.95   $120.90  
  7 purchase totals = $932.07       $1,029.7346   $1,029.73   $1,029.70   $1,029.70