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 $54.64   3.630%   $56.6234   $56.62   $56.60   $56.60  
  Purchase #2 $74.34   4.358%   $77.5797   $77.58   $77.60   $77.60  
  Purchase #3 $8.92   10.373%   $9.8453   $9.85   $9.85   $9.80  
  Purchase #4 $182.37   13.844%   $207.6173   $207.62   $207.60   $207.60  
  Purchase #5 $121.66   9.157%   $132.8004   $132.80   $132.80   $132.80  
  Purchase #6 $185.84   3.582%   $192.4968   $192.50   $192.50   $192.50  
  Purchase #7 $244.31   8.294%   $264.5731   $264.57   $264.55   $264.60  
  7 purchase totals = $872.08       $941.5360   $941.54   $941.50   $941.50