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 $72.77   5.202%   $76.5555   $76.56   $76.55   $76.60  
  Purchase #2 $223.43   11.325%   $248.7334   $248.73   $248.75   $248.70  
  Purchase #3 $36.76   7.366%   $39.4677   $39.47   $39.45   $39.50  
  Purchase #4 $116.85   13.468%   $132.5874   $132.59   $132.60   $132.60  
  Purchase #5 $93.43   10.770%   $103.4924   $103.49   $103.50   $103.50  
  Purchase #6 $113.28   3.658%   $117.4238   $117.42   $117.40   $117.40  
  Purchase #7 $160.73   10.826%   $178.1306   $178.13   $178.15   $178.10  
  7 purchase totals = $817.25       $896.3908   $896.39   $896.40   $896.40