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 $153.35   10.279%   $169.1128   $169.11   $169.10   $169.10  
  Purchase #2 $232.36   5.288%   $244.6472   $244.65   $244.65   $244.60  
  Purchase #3 $35.87   3.718%   $37.2036   $37.20   $37.20   $37.20  
  Purchase #4 $89.99   8.726%   $97.8425   $97.84   $97.85   $97.80  
  Purchase #5 $185.67   5.593%   $196.0545   $196.05   $196.05   $196.10  
  Purchase #6 $56.66   6.797%   $60.5112   $60.51   $60.50   $60.50  
  Purchase #7 $45.53   9.525%   $49.8667   $49.87   $49.85   $49.90  
  7 purchase totals = $799.43       $855.2385   $855.23   $855.20   $855.20