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 $232.35   10.301%   $256.2844   $256.28   $256.30   $256.30  
  Purchase #2 $21.42   5.840%   $22.6709   $22.67   $22.65   $22.70  
  Purchase #3 $67.68   8.459%   $73.4051   $73.41   $73.40   $73.40  
  Purchase #4 $52.95   9.465%   $57.9617   $57.96   $57.95   $58.00  
  Purchase #5 $78.46   11.406%   $87.4091   $87.41   $87.40   $87.40  
  Purchase #6 $196.74   6.750%   $210.02   $210.02   $210.00   $210.00  
  Purchase #7 $225.37   10.669%   $249.4147   $249.41   $249.40   $249.40  
  7 purchase totals = $874.97       $957.1659   $957.16   $957.10   $957.20