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 $164.63   13.552%   $186.9407   $186.94   $186.95   $186.90  
  Purchase #2 $206.66   13.621%   $234.8092   $234.81   $234.80   $234.80  
  Purchase #3 $160.62   9.755%   $176.2885   $176.29   $176.30   $176.30  
  Purchase #4 $232.71   11.859%   $260.3071   $260.31   $260.30   $260.30  
  Purchase #5 $244.31   8.256%   $264.4802   $264.48   $264.50   $264.50  
  Purchase #6 $77.99   9.593%   $85.4716   $85.47   $85.45   $85.50  
  Purchase #7 $116.29   5.726%   $122.9488   $122.95   $122.95   $122.90  
  7 purchase totals = $1,203.21       $1,331.2461   $1,331.25   $1,331.25   $1,331.20