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 $62.92   4.421%   $65.7017   $65.70   $65.70   $65.70  
  Purchase #2 $182.30   5.659%   $192.6164   $192.62   $192.60   $192.60  
  Purchase #3 $113.64   11.477%   $126.6825   $126.68   $126.70   $126.70  
  Purchase #4 $215.32   5.214%   $226.5468   $226.55   $226.55   $226.50  
  Purchase #5 $99.94   12.864%   $112.7963   $112.80   $112.80   $112.80  
  Purchase #6 $158.92   6.111%   $168.6316   $168.63   $168.65   $168.60  
  Purchase #7 $133.92   11.226%   $148.9539   $148.95   $148.95   $149.00  
  7 purchase totals = $966.96       $1,041.9292   $1,041.93   $1,041.95   $1,041.90