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 $204.63   7.613%   $220.2085   $220.21   $220.20   $220.20  
  Purchase #2 $88.51   5.698%   $93.5533   $93.55   $93.55   $93.60  
  Purchase #3 $117.68   3.153%   $121.3905   $121.39   $121.40   $121.40  
  Purchase #4 $85.91   10.220%   $94.69   $94.69   $94.70   $94.70  
  Purchase #5 $134.91   4.562%   $141.0646   $141.06   $141.05   $141.10  
  Purchase #6 $162.42   6.433%   $172.8685   $172.87   $172.85   $172.90  
  Purchase #7 $242.55   7.186%   $259.9796   $259.98   $260.00   $260.00  
  7 purchase totals = $1,036.61       $1,103.7550   $1,103.75   $1,103.75   $1,103.90