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 $88.60   9.750%   $97.2385   $97.24   $97.25   $97.20  
  Purchase #2 $60.35   12.671%   $67.9969   $68.00   $68.00   $68.00  
  Purchase #3 $232.99   8.379%   $252.5122   $252.51   $252.50   $252.50  
  Purchase #4 $158.78   12.479%   $178.5942   $178.59   $178.60   $178.60  
  Purchase #5 $153.43   9.855%   $168.5505   $168.55   $168.55   $168.60  
  Purchase #6 $34.28   6.507%   $36.5106   $36.51   $36.50   $36.50  
  Purchase #7 $132.32   9.457%   $144.8335   $144.83   $144.85   $144.80  
  7 purchase totals = $860.75       $946.2364   $946.23   $946.25   $946.20