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 $42.71   12.234%   $47.9351   $47.94   $47.95   $47.90  
  Purchase #2 $174.44   7.735%   $187.9329   $187.93   $187.95   $187.90  
  Purchase #3 $83.26   3.241%   $85.9585   $85.96   $85.95   $86.00  
  Purchase #4 $91.95   5.567%   $97.0689   $97.07   $97.05   $97.10  
  Purchase #5 $166.39   11.528%   $185.5714   $185.57   $185.55   $185.60  
  Purchase #6 $147.82   4.416%   $154.3477   $154.35   $154.35   $154.30  
  Purchase #7 $181.68   8.122%   $196.436   $196.44   $196.45   $196.40  
  7 purchase totals = $888.25       $955.2505   $955.26   $955.25   $955.20