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 $119.66   12.488%   $134.6031   $134.60   $134.60   $134.60  
  Purchase #2 $127.30   13.410%   $144.3709   $144.37   $144.35   $144.40  
  Purchase #3 $230.69   10.196%   $254.2112   $254.21   $254.20   $254.20  
  Purchase #4 $37.82   9.201%   $41.2998   $41.30   $41.30   $41.30  
  Purchase #5 $23.50   4.632%   $24.5885   $24.59   $24.60   $24.60  
  Purchase #6 $148.25   5.723%   $156.7343   $156.73   $156.75   $156.70  
  Purchase #7 $245.38   13.708%   $279.0167   $279.02   $279.00   $279.00  
  7 purchase totals = $932.60       $1,034.8245   $1,034.82   $1,034.80   $1,034.80