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 $92.68   12.807%   $104.5495   $104.55   $104.55   $104.50  
  Purchase #2 $207.30   7.282%   $222.3956   $222.40   $222.40   $222.40  
  Purchase #3 $151.28   3.518%   $156.602   $156.60   $156.60   $156.60  
  Purchase #4 $81.77   3.753%   $84.8388   $84.84   $84.85   $84.80  
  Purchase #5 $184.86   13.665%   $210.1211   $210.12   $210.10   $210.10  
  Purchase #6 $162.87   6.733%   $173.836   $173.84   $173.85   $173.80  
  Purchase #7 $203.34   10.146%   $223.9709   $223.97   $223.95   $224.00  
  7 purchase totals = $1,084.10       $1,176.3139   $1,176.32   $1,176.30   $1,176.20