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 $68.43   10.829%   $75.8403   $75.84   $75.85   $75.80  
  Purchase #2 $101.42   13.634%   $115.2476   $115.25   $115.25   $115.20  
  Purchase #3 $103.30   6.332%   $109.841   $109.84   $109.85   $109.80  
  Purchase #4 $97.53   10.430%   $107.7024   $107.70   $107.70   $107.70  
  Purchase #5 $182.77   13.399%   $207.2594   $207.26   $207.25   $207.30  
  Purchase #6 $200.61   6.371%   $213.3909   $213.39   $213.40   $213.40  
  Purchase #7 $72.70   12.758%   $81.9751   $81.98   $82.00   $82.00  
  7 purchase totals = $826.76       $911.2567   $911.26   $911.30   $911.20