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 $37.28   11.159%   $41.4401   $41.44   $41.45   $41.40  
  Purchase #2 $92.64   5.196%   $97.4536   $97.45   $97.45   $97.50  
  Purchase #3 $40.32   7.516%   $43.3505   $43.35   $43.35   $43.40  
  Purchase #4 $161.65   8.584%   $175.526   $175.53   $175.55   $175.50  
  Purchase #5 $202.98   5.712%   $214.5742   $214.57   $214.55   $214.60  
  Purchase #6 $91.78   13.585%   $104.2483   $104.25   $104.25   $104.20  
  Purchase #7 $94.30   12.740%   $106.3138   $106.31   $106.30   $106.30  
  7 purchase totals = $720.95       $782.9065   $782.90   $782.90   $782.90