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 $62.47   12.751%   $70.4355   $70.44   $70.45   $70.40  
  Purchase #2 $18.95   4.108%   $19.7285   $19.73   $19.75   $19.70  
  Purchase #3 $156.60   4.204%   $163.1835   $163.18   $163.20   $163.20  
  Purchase #4 $101.50   4.597%   $106.166   $106.17   $106.15   $106.20  
  Purchase #5 $201.99   8.652%   $219.4662   $219.47   $219.45   $219.50  
  Purchase #6 $142.27   3.512%   $147.2665   $147.27   $147.25   $147.30  
  Purchase #7 $182.29   4.793%   $191.0272   $191.03   $191.05   $191.00  
  7 purchase totals = $866.07       $917.2734   $917.29   $917.30   $917.30