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 $188.59   11.749%   $210.7474   $210.75   $210.75   $210.70  
  Purchase #2 $81.95   7.873%   $88.4019   $88.40   $88.40   $88.40  
  Purchase #3 $78.49   7.116%   $84.0753   $84.08   $84.10   $84.10  
  Purchase #4 $205.69   4.109%   $214.1418   $214.14   $214.15   $214.10  
  Purchase #5 $90.32   4.462%   $94.3501   $94.35   $94.35   $94.40  
  Purchase #6 $161.48   13.859%   $183.8595   $183.86   $183.85   $183.90  
  Purchase #7 $93.65   6.181%   $99.4385   $99.44   $99.45   $99.40  
  7 purchase totals = $900.17       $975.0145   $975.02   $975.05   $975.00