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 $227.62   10.653%   $251.8684   $251.87   $251.85   $251.90  
  Purchase #2 $164.29   7.706%   $176.9502   $176.95   $176.95   $177.00  
  Purchase #3 $5.90   7.244%   $6.3274   $6.33   $6.35   $6.30  
  Purchase #4 $214.33   8.614%   $232.7924   $232.79   $232.80   $232.80  
  Purchase #5 $119.25   9.331%   $130.3772   $130.38   $130.40   $130.40  
  Purchase #6 $176.59   10.667%   $195.4269   $195.43   $195.45   $195.40  
  Purchase #7 $182.65   5.660%   $192.988   $192.99   $193.00   $193.00  
  7 purchase totals = $1,090.63       $1,186.7305   $1,186.74   $1,186.80   $1,186.80