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 $85.40   12.343%   $95.9409   $95.94   $95.95   $95.90  
  Purchase #2 $96.93   9.247%   $105.8931   $105.89   $105.90   $105.90  
  Purchase #3 $219.59   7.459%   $235.9692   $235.97   $235.95   $236.00  
  Purchase #4 $176.74   11.467%   $197.0068   $197.01   $197.00   $197.00  
  Purchase #5 $148.69   4.709%   $155.6918   $155.69   $155.70   $155.70  
  Purchase #6 $22.58   9.287%   $24.677   $24.68   $24.70   $24.70  
  Purchase #7 $162.29   13.553%   $184.2852   $184.29   $184.30   $184.30  
  7 purchase totals = $912.22       $999.4640   $999.47   $999.50   $999.50