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 $126.47   10.198%   $139.3674   $139.37   $139.35   $139.40  
  Purchase #2 $102.54   4.194%   $106.8405   $106.84   $106.85   $106.80  
  Purchase #3 $249.80   6.157%   $265.1802   $265.18   $265.20   $265.20  
  Purchase #4 $121.58   4.845%   $127.4706   $127.47   $127.45   $127.50  
  Purchase #5 $91.67   5.423%   $96.6413   $96.64   $96.65   $96.60  
  Purchase #6 $95.93   3.209%   $99.0084   $99.01   $99.00   $99.00  
  Purchase #7 $89.54   3.285%   $92.4814   $92.48   $92.50   $92.50  
  7 purchase totals = $877.53       $926.9898   $926.99   $927.00   $927.00