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 $62.98   7.771%   $67.8742   $67.87   $67.85   $67.90  
  Purchase #2 $80.84   11.870%   $90.4357   $90.44   $90.45   $90.40  
  Purchase #3 $135.95   3.485%   $140.6879   $140.69   $140.70   $140.70  
  Purchase #4 $216.86   7.744%   $233.6536   $233.65   $233.65   $233.70  
  Purchase #5 $187.78   9.383%   $205.3994   $205.40   $205.40   $205.40  
  Purchase #6 $49.40   4.707%   $51.7253   $51.73   $51.75   $51.70  
  Purchase #7 $70.71   3.418%   $73.1269   $73.13   $73.15   $73.10  
  7 purchase totals = $804.52       $862.9030   $862.91   $862.95   $862.90