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 $103.48   13.783%   $117.7426   $117.74   $117.75   $117.70  
  Purchase #2 $106.39   6.197%   $112.983   $112.98   $113.00   $113.00  
  Purchase #3 $76.85   7.828%   $82.8658   $82.87   $82.85   $82.90  
  Purchase #4 $224.91   5.643%   $237.6017   $237.60   $237.60   $237.60  
  Purchase #5 $124.63   13.121%   $140.9827   $140.98   $141.00   $141.00  
  Purchase #6 $247.73   4.188%   $258.1049   $258.10   $258.10   $258.10  
  Purchase #7 $60.90   9.665%   $66.786   $66.79   $66.80   $66.80  
  7 purchase totals = $944.89       $1,017.0667   $1,017.06   $1,017.10   $1,017.10