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 $30.66   6.345%   $32.6054   $32.61   $32.60   $32.60  
  Purchase #2 $208.98   12.622%   $235.3575   $235.36   $235.35   $235.40  
  Purchase #3 $174.36   4.446%   $182.112   $182.11   $182.10   $182.10  
  Purchase #4 $84.66   4.247%   $88.2555   $88.26   $88.25   $88.30  
  Purchase #5 $165.54   10.516%   $182.9482   $182.95   $182.95   $182.90  
  Purchase #6 $186.32   4.763%   $195.1944   $195.19   $195.20   $195.20  
  Purchase #7 $87.59   12.834%   $98.8313   $98.83   $98.85   $98.80  
  7 purchase totals = $938.11       $1,015.3043   $1,015.31   $1,015.30   $1,015.30