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 $98.78   7.316%   $106.0067   $106.01   $106.00   $106.00  
  Purchase #2 $67.89   11.332%   $75.5833   $75.58   $75.60   $75.60  
  Purchase #3 $65.59   3.646%   $67.9814   $67.98   $68.00   $68.00  
  Purchase #4 $128.28   3.231%   $132.4247   $132.42   $132.40   $132.40  
  Purchase #5 $124.85   9.717%   $136.9817   $136.98   $137.00   $137.00  
  Purchase #6 $157.59   8.600%   $171.1427   $171.14   $171.15   $171.10  
  Purchase #7 $239.66   8.237%   $259.4008   $259.40   $259.40   $259.40  
  7 purchase totals = $882.64       $949.5213   $949.51   $949.55   $949.50