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 $206.94   9.832%   $227.2863   $227.29   $227.30   $227.30  
  Purchase #2 $229.55   11.780%   $256.591   $256.59   $256.60   $256.60  
  Purchase #3 $198.85   3.736%   $206.279   $206.28   $206.30   $206.30  
  Purchase #4 $177.42   5.663%   $187.4673   $187.47   $187.45   $187.50  
  Purchase #5 $67.75   11.733%   $75.6991   $75.70   $75.70   $75.70  
  Purchase #6 $225.82   8.221%   $244.3847   $244.38   $244.40   $244.40  
  Purchase #7 $175.92   5.716%   $185.9756   $185.98   $186.00   $186.00  
  7 purchase totals = $1,282.25       $1,383.6830   $1,383.69   $1,383.75   $1,383.80