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 $79.44   9.202%   $86.7501   $86.75   $86.75   $86.80  
  Purchase #2 $89.61   6.209%   $95.1739   $95.17   $95.15   $95.20  
  Purchase #3 $194.48   9.263%   $212.4947   $212.49   $212.50   $212.50  
  Purchase #4 $246.59   8.372%   $267.2345   $267.23   $267.25   $267.20  
  Purchase #5 $67.57   5.487%   $71.2776   $71.28   $71.30   $71.30  
  Purchase #6 $184.79   7.103%   $197.9156   $197.92   $197.90   $197.90  
  Purchase #7 $99.49   5.372%   $104.8346   $104.83   $104.85   $104.80  
  7 purchase totals = $961.97       $1,035.6810   $1,035.67   $1,035.70   $1,035.70