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 $94.46   3.251%   $97.5309   $97.53   $97.55   $97.50  
  Purchase #2 $166.27   11.416%   $185.2514   $185.25   $185.25   $185.30  
  Purchase #3 $88.34   4.749%   $92.5353   $92.54   $92.55   $92.50  
  Purchase #4 $173.63   10.296%   $191.5069   $191.51   $191.50   $191.50  
  Purchase #5 $243.28   6.452%   $258.9764   $258.98   $259.00   $259.00  
  Purchase #6 $182.47   10.351%   $201.3575   $201.36   $201.35   $201.40  
  Purchase #7 $131.71   3.793%   $136.7058   $136.71   $136.70   $136.70  
  7 purchase totals = $1,080.16       $1,163.8642   $1,163.88   $1,163.90   $1,163.90