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 $233.82   8.185%   $252.9582   $252.96   $252.95   $253.00  
  Purchase #2 $128.41   4.307%   $133.9406   $133.94   $133.95   $133.90  
  Purchase #3 $98.25   13.192%   $111.2111   $111.21   $111.20   $111.20  
  Purchase #4 $202.84   13.217%   $229.6494   $229.65   $229.65   $229.60  
  Purchase #5 $209.79   8.381%   $227.3725   $227.37   $227.35   $227.40  
  Purchase #6 $115.91   6.667%   $123.6377   $123.64   $123.65   $123.60  
  Purchase #7 $134.30   6.280%   $142.734   $142.73   $142.75   $142.70  
  7 purchase totals = $1,123.32       $1,221.5035   $1,221.50   $1,221.50   $1,221.40