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 $74.76   10.362%   $82.5066   $82.51   $82.50   $82.50  
  Purchase #2 $23.75   3.477%   $24.5758   $24.58   $24.60   $24.60  
  Purchase #3 $67.62   5.238%   $71.1619   $71.16   $71.15   $71.20  
  Purchase #4 $126.76   3.263%   $130.8962   $130.90   $130.90   $130.90  
  Purchase #5 $193.79   6.719%   $206.8108   $206.81   $206.80   $206.80  
  Purchase #6 $238.36   5.395%   $251.2195   $251.22   $251.20   $251.20  
  Purchase #7 $94.77   6.642%   $101.0646   $101.06   $101.05   $101.10  
  7 purchase totals = $819.81       $868.2354   $868.24   $868.20   $868.30