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 $195.90   5.349%   $206.3787   $206.38   $206.40   $206.40  
  Purchase #2 $214.34   6.501%   $228.2742   $228.27   $228.25   $228.30  
  Purchase #3 $112.45   7.399%   $120.7702   $120.77   $120.75   $120.80  
  Purchase #4 $20.25   3.208%   $20.8996   $20.90   $20.90   $20.90  
  Purchase #5 $191.91   10.188%   $211.4618   $211.46   $211.45   $211.50  
  Purchase #6 $88.30   6.871%   $94.3671   $94.37   $94.35   $94.40  
  Purchase #7 $93.53   4.600%   $97.8324   $97.83   $97.85   $97.80  
  7 purchase totals = $916.68       $979.9840   $979.98   $979.95   $980.10