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 $124.63   13.326%   $141.2382   $141.24   $141.25   $141.20  
  Purchase #2 $234.39   4.700%   $245.4063   $245.41   $245.40   $245.40  
  Purchase #3 $124.64   12.772%   $140.559   $140.56   $140.55   $140.60  
  Purchase #4 $83.55   9.232%   $91.2633   $91.26   $91.25   $91.30  
  Purchase #5 $65.82   13.555%   $74.7419   $74.74   $74.75   $74.70  
  Purchase #6 $104.26   11.478%   $116.227   $116.23   $116.25   $116.20  
  Purchase #7 $186.29   4.476%   $194.6283   $194.63   $194.65   $194.60  
  7 purchase totals = $923.58       $1,004.0640   $1,004.07   $1,004.10   $1,004.00