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 $6.82   4.639%   $7.1364   $7.14   $7.15   $7.10  
  Purchase #2 $135.30   6.473%   $144.058   $144.06   $144.05   $144.10  
  Purchase #3 $131.29   6.693%   $140.0772   $140.08   $140.10   $140.10  
  Purchase #4 $231.77   5.429%   $244.3528   $244.35   $244.35   $244.40  
  Purchase #5 $72.86   6.681%   $77.7278   $77.73   $77.75   $77.70  
  Purchase #6 $199.55   11.773%   $223.043   $223.04   $223.05   $223.00  
  Purchase #7 $195.38   13.117%   $221.008   $221.01   $221.00   $221.00  
  7 purchase totals = $972.97       $1,057.4032   $1,057.41   $1,057.45   $1,057.40