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 $213.81   13.834%   $243.3885   $243.39   $243.40   $243.40  
  Purchase #2 $117.69   13.326%   $133.3734   $133.37   $133.35   $133.40  
  Purchase #3 $141.84   12.423%   $159.4608   $159.46   $159.45   $159.50  
  Purchase #4 $165.34   7.157%   $177.1734   $177.17   $177.15   $177.20  
  Purchase #5 $57.97   7.812%   $62.4986   $62.50   $62.50   $62.50  
  Purchase #6 $199.33   7.793%   $214.8638   $214.86   $214.85   $214.90  
  Purchase #7 $87.75   7.330%   $94.1821   $94.18   $94.20   $94.20  
  7 purchase totals = $983.73       $1,084.9406   $1,084.93   $1,084.90   $1,085.10