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 $247.37   5.455%   $260.864   $260.86   $260.85   $260.90  
  Purchase #2 $185.62   13.533%   $210.74   $210.74   $210.75   $210.70  
  Purchase #3 $76.95   8.352%   $83.3769   $83.38   $83.40   $83.40  
  Purchase #4 $132.99   6.292%   $141.3577   $141.36   $141.35   $141.40  
  Purchase #5 $228.83   5.166%   $240.6514   $240.65   $240.65   $240.70  
  Purchase #6 $63.90   9.546%   $69.9999   $70.00   $70.00   $70.00  
  Purchase #7 $56.48   12.665%   $63.6332   $63.63   $63.65   $63.60  
  7 purchase totals = $992.14       $1,070.6231   $1,070.62   $1,070.65   $1,070.70