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 $25.26   11.562%   $28.1806   $28.18   $28.20   $28.20  
  Purchase #2 $116.69   13.639%   $132.6053   $132.61   $132.60   $132.60  
  Purchase #3 $7.89   7.846%   $8.509   $8.51   $8.50   $8.50  
  Purchase #4 $165.65   13.126%   $187.3932   $187.39   $187.40   $187.40  
  Purchase #5 $193.40   12.121%   $216.842   $216.84   $216.85   $216.80  
  Purchase #6 $118.44   7.447%   $127.2602   $127.26   $127.25   $127.30  
  Purchase #7 $232.30   8.286%   $251.5484   $251.55   $251.55   $251.50  
  7 purchase totals = $859.63       $952.3387   $952.34   $952.35   $952.30