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 $55.99   8.659%   $60.8382   $60.84   $60.85   $60.80  
  Purchase #2 $213.33   9.133%   $232.8134   $232.81   $232.80   $232.80  
  Purchase #3 $62.31   11.161%   $69.2644   $69.26   $69.25   $69.30  
  Purchase #4 $182.64   12.118%   $204.7723   $204.77   $204.75   $204.80  
  Purchase #5 $165.31   5.296%   $174.0648   $174.06   $174.05   $174.10  
  Purchase #6 $156.94   10.545%   $173.4893   $173.49   $173.50   $173.50  
  Purchase #7 $112.41   11.415%   $125.2416   $125.24   $125.25   $125.20  
  7 purchase totals = $948.93       $1,040.4840   $1,040.47   $1,040.45   $1,040.50