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 $61.89   8.741%   $67.2998   $67.30   $67.30   $67.30  
  Purchase #2 $248.57   11.491%   $277.1332   $277.13   $277.15   $277.10  
  Purchase #3 $249.67   13.443%   $283.2331   $283.23   $283.25   $283.20  
  Purchase #4 $124.34   6.468%   $132.3823   $132.38   $132.40   $132.40  
  Purchase #5 $169.77   10.747%   $188.0152   $188.02   $188.00   $188.00  
  Purchase #6 $12.55   8.258%   $13.5864   $13.59   $13.60   $13.60  
  Purchase #7 $34.99   6.157%   $37.1443   $37.14   $37.15   $37.10  
  7 purchase totals = $901.78       $998.7943   $998.79   $998.85   $998.70