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 $74.59   13.783%   $84.8707   $84.87   $84.85   $84.90  
  Purchase #2 $218.30   8.447%   $236.7398   $236.74   $236.75   $236.70  
  Purchase #3 $185.64   6.385%   $197.4931   $197.49   $197.50   $197.50  
  Purchase #4 $59.75   3.138%   $61.625   $61.63   $61.65   $61.60  
  Purchase #5 $165.74   13.702%   $188.4497   $188.45   $188.45   $188.40  
  Purchase #6 $21.29   11.512%   $23.7409   $23.74   $23.75   $23.70  
  Purchase #7 $241.80   11.515%   $269.6433   $269.64   $269.65   $269.60  
  7 purchase totals = $967.11       $1,062.5625   $1,062.56   $1,062.60   $1,062.40