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 $28.88   11.683%   $32.2541   $32.25   $32.25   $32.30  
  Purchase #2 $214.28   9.347%   $234.3088   $234.31   $234.30   $234.30  
  Purchase #3 $239.27   12.684%   $269.619   $269.62   $269.60   $269.60  
  Purchase #4 $27.30   11.792%   $30.5192   $30.52   $30.50   $30.50  
  Purchase #5 $176.33   10.616%   $195.0492   $195.05   $195.05   $195.00  
  Purchase #6 $182.84   13.742%   $207.9659   $207.97   $207.95   $208.00  
  Purchase #7 $246.47   6.550%   $262.6138   $262.61   $262.60   $262.60  
  7 purchase totals = $1,115.37       $1,232.3300   $1,232.33   $1,232.25   $1,232.30