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 $161.49   10.569%   $178.5579   $178.56   $178.55   $178.60  
  Purchase #2 $64.60   13.236%   $73.1505   $73.15   $73.15   $73.20  
  Purchase #3 $95.27   4.663%   $99.7124   $99.71   $99.70   $99.70  
  Purchase #4 $221.91   5.369%   $233.8243   $233.82   $233.80   $233.80  
  Purchase #5 $122.47   9.810%   $134.4843   $134.48   $134.50   $134.50  
  Purchase #6 $119.72   8.204%   $129.5418   $129.54   $129.55   $129.50  
  Purchase #7 $239.36   6.168%   $254.1237   $254.12   $254.10   $254.10  
  7 purchase totals = $1,024.82       $1,103.3949   $1,103.38   $1,103.35   $1,103.40