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 $206.51   13.185%   $233.7383   $233.74   $233.75   $233.70  
  Purchase #2 $168.41   7.665%   $181.3186   $181.32   $181.30   $181.30  
  Purchase #3 $104.76   12.395%   $117.745   $117.75   $117.75   $117.70  
  Purchase #4 $229.72   10.223%   $253.2043   $253.20   $253.20   $253.20  
  Purchase #5 $189.29   10.227%   $208.6487   $208.65   $208.65   $208.60  
  Purchase #6 $188.40   8.230%   $203.9053   $203.91   $203.90   $203.90  
  Purchase #7 $155.78   4.582%   $162.9178   $162.92   $162.90   $162.90  
  7 purchase totals = $1,242.87       $1,361.4780   $1,361.49   $1,361.45   $1,361.30