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 $248.63   11.421%   $277.026   $277.03   $277.05   $277.00  
  Purchase #2 $30.36   7.340%   $32.5884   $32.59   $32.60   $32.60  
  Purchase #3 $221.83   9.546%   $243.0059   $243.01   $243.00   $243.00  
  Purchase #4 $216.91   11.311%   $241.4447   $241.44   $241.45   $241.40  
  Purchase #5 $204.94   4.256%   $213.6622   $213.66   $213.65   $213.70  
  Purchase #6 $183.84   4.778%   $192.6239   $192.62   $192.60   $192.60  
  Purchase #7 $24.92   4.755%   $26.1049   $26.10   $26.10   $26.10  
  7 purchase totals = $1,131.43       $1,226.4560   $1,226.45   $1,226.45   $1,226.40