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 $219.53   6.276%   $233.3077   $233.31   $233.30   $233.30  
  Purchase #2 $249.28   8.862%   $271.3712   $271.37   $271.35   $271.40  
  Purchase #3 $190.76   7.218%   $204.5291   $204.53   $204.55   $204.50  
  Purchase #4 $222.91   7.647%   $239.9559   $239.96   $239.95   $240.00  
  Purchase #5 $187.67   11.363%   $208.9949   $208.99   $209.00   $209.00  
  Purchase #6 $46.69   5.742%   $49.3709   $49.37   $49.35   $49.40  
  Purchase #7 $88.96   9.123%   $97.0758   $97.08   $97.10   $97.10  
  7 purchase totals = $1,205.80       $1,304.6055   $1,304.61   $1,304.60   $1,304.70