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 $58.37   5.477%   $61.5669   $61.57   $61.55   $61.60  
  Purchase #2 $230.79   11.758%   $257.9263   $257.93   $257.95   $257.90  
  Purchase #3 $147.67   7.659%   $158.98   $158.98   $159.00   $159.00  
  Purchase #4 $24.63   11.405%   $27.4391   $27.44   $27.45   $27.40  
  Purchase #5 $30.78   9.569%   $33.7253   $33.73   $33.75   $33.70  
  Purchase #6 $67.28   9.484%   $73.6608   $73.66   $73.65   $73.70  
  Purchase #7 $241.96   8.671%   $262.9404   $262.94   $262.95   $262.90  
  7 purchase totals = $801.48       $876.2388   $876.25   $876.30   $876.20