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 $72.57   6.553%   $77.3255   $77.33   $77.35   $77.30  
  Purchase #2 $132.61   3.248%   $136.9172   $136.92   $136.90   $136.90  
  Purchase #3 $206.62   12.653%   $232.7636   $232.76   $232.75   $232.80  
  Purchase #4 $171.98   7.587%   $185.0281   $185.03   $185.05   $185.00  
  Purchase #5 $58.41   9.657%   $64.0507   $64.05   $64.05   $64.10  
  Purchase #6 $208.59   13.465%   $236.6766   $236.68   $236.70   $236.70  
  Purchase #7 $28.87   12.457%   $32.4663   $32.47   $32.45   $32.50  
  7 purchase totals = $879.65       $965.2280   $965.24   $965.25   $965.30