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 $88.84   7.717%   $95.6958   $95.70   $95.70   $95.70  
  Purchase #2 $54.26   3.563%   $56.1933   $56.19   $56.20   $56.20  
  Purchase #3 $223.30   11.272%   $248.4704   $248.47   $248.45   $248.50  
  Purchase #4 $68.43   6.648%   $72.9792   $72.98   $73.00   $73.00  
  Purchase #5 $92.25   5.524%   $97.3459   $97.35   $97.35   $97.30  
  Purchase #6 $96.57   13.266%   $109.381   $109.38   $109.40   $109.40  
  Purchase #7 $90.69   4.374%   $94.6568   $94.66   $94.65   $94.70  
  7 purchase totals = $714.34       $774.7224   $774.73   $774.75   $774.80