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 $67.99   12.575%   $76.5397   $76.54   $76.55   $76.50  
  Purchase #2 $242.76   3.533%   $251.3367   $251.34   $251.35   $251.30  
  Purchase #3 $63.95   10.658%   $70.7658   $70.77   $70.75   $70.80  
  Purchase #4 $62.47   5.118%   $65.6672   $65.67   $65.65   $65.70  
  Purchase #5 $117.36   7.650%   $126.338   $126.34   $126.35   $126.30  
  Purchase #6 $147.39   11.617%   $164.5123   $164.51   $164.50   $164.50  
  Purchase #7 $151.42   3.232%   $156.3139   $156.31   $156.30   $156.30  
  7 purchase totals = $853.34       $911.4736   $911.48   $911.45   $911.40