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 $101.98   12.359%   $114.5837   $114.58   $114.60   $114.60  
  Purchase #2 $215.82   6.835%   $230.5713   $230.57   $230.55   $230.60  
  Purchase #3 $116.85   7.767%   $125.9257   $125.93   $125.95   $125.90  
  Purchase #4 $42.57   12.661%   $47.9598   $47.96   $47.95   $48.00  
  Purchase #5 $230.45   6.399%   $245.1965   $245.20   $245.20   $245.20  
  Purchase #6 $215.47   5.589%   $227.5126   $227.51   $227.50   $227.50  
  Purchase #7 $75.89   12.853%   $85.6441   $85.64   $85.65   $85.60  
  7 purchase totals = $999.03       $1,077.3937   $1,077.39   $1,077.40   $1,077.40