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 $202.58   10.806%   $224.4708   $224.47   $224.45   $224.50  
  Purchase #2 $80.73   11.733%   $90.2021   $90.20   $90.20   $90.20  
  Purchase #3 $192.43   3.865%   $199.8674   $199.87   $199.85   $199.90  
  Purchase #4 $86.80   10.179%   $95.6354   $95.64   $95.65   $95.60  
  Purchase #5 $198.54   5.560%   $209.5788   $209.58   $209.60   $209.60  
  Purchase #6 $132.74   12.570%   $149.4254   $149.43   $149.45   $149.40  
  Purchase #7 $58.83   9.165%   $64.2218   $64.22   $64.20   $64.20  
  7 purchase totals = $952.65       $1,033.4017   $1,033.41   $1,033.40   $1,033.40