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 $244.73   7.659%   $263.4739   $263.47   $263.45   $263.50  
  Purchase #2 $88.50   12.711%   $99.7492   $99.75   $99.75   $99.70  
  Purchase #3 $62.84   11.127%   $69.8322   $69.83   $69.85   $69.80  
  Purchase #4 $173.62   12.424%   $195.1905   $195.19   $195.20   $195.20  
  Purchase #5 $93.39   3.621%   $96.7717   $96.77   $96.75   $96.80  
  Purchase #6 $188.55   4.788%   $197.5778   $197.58   $197.60   $197.60  
  Purchase #7 $110.64   11.747%   $123.6369   $123.64   $123.65   $123.60  
  7 purchase totals = $962.27       $1,046.2322   $1,046.23   $1,046.25   $1,046.20