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 $234.62   7.342%   $251.8458   $251.85   $251.85   $251.80  
  Purchase #2 $201.95   6.560%   $215.1979   $215.20   $215.20   $215.20  
  Purchase #3 $104.85   8.151%   $113.3963   $113.40   $113.40   $113.40  
  Purchase #4 $52.51   9.772%   $57.6413   $57.64   $57.65   $57.60  
  Purchase #5 $171.56   9.851%   $188.4604   $188.46   $188.45   $188.50  
  Purchase #6 $6.55   3.712%   $6.7931   $6.79   $6.80   $6.80  
  Purchase #7 $194.27   7.344%   $208.5372   $208.54   $208.55   $208.50  
  7 purchase totals = $966.31       $1,041.8720   $1,041.88   $1,041.90   $1,041.80