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 $202.84   8.796%   $220.6818   $220.68   $220.70   $220.70  
  Purchase #2 $154.26   9.282%   $168.5784   $168.58   $168.60   $168.60  
  Purchase #3 $130.96   10.169%   $144.2773   $144.28   $144.30   $144.30  
  Purchase #4 $239.59   11.604%   $267.392   $267.39   $267.40   $267.40  
  Purchase #5 $48.68   8.444%   $52.7905   $52.79   $52.80   $52.80  
  Purchase #6 $189.90   9.534%   $208.0051   $208.01   $208.00   $208.00  
  Purchase #7 $17.43   7.708%   $18.7735   $18.77   $18.75   $18.80  
  7 purchase totals = $983.66       $1,080.4986   $1,080.50   $1,080.55   $1,080.60