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 $101.87   5.620%   $107.5951   $107.60   $107.60   $107.60  
  Purchase #2 $70.61   8.427%   $76.5603   $76.56   $76.55   $76.60  
  Purchase #3 $161.59   5.824%   $171.001   $171.00   $171.00   $171.00  
  Purchase #4 $118.82   4.672%   $124.3713   $124.37   $124.35   $124.40  
  Purchase #5 $239.60   11.698%   $267.6284   $267.63   $267.65   $267.60  
  Purchase #6 $60.53   4.781%   $63.4239   $63.42   $63.40   $63.40  
  Purchase #7 $190.55   7.781%   $205.3767   $205.38   $205.40   $205.40  
  7 purchase totals = $943.57       $1,015.9567   $1,015.96   $1,015.95   $1,016.00