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 $225.76   4.517%   $235.9576   $235.96   $235.95   $236.00  
  Purchase #2 $168.76   10.630%   $186.6992   $186.70   $186.70   $186.70  
  Purchase #3 $237.26   8.530%   $257.4983   $257.50   $257.50   $257.50  
  Purchase #4 $114.69   11.119%   $127.4424   $127.44   $127.45   $127.40  
  Purchase #5 $5.63   5.519%   $5.9407   $5.94   $5.95   $5.90  
  Purchase #6 $135.86   13.549%   $154.2677   $154.27   $154.25   $154.30  
  Purchase #7 $93.88   7.560%   $100.9773   $100.98   $101.00   $101.00  
  7 purchase totals = $981.84       $1,068.7832   $1,068.79   $1,068.80   $1,068.80