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 $152.80   11.590%   $170.5095   $170.51   $170.50   $170.50  
  Purchase #2 $17.26   8.868%   $18.7906   $18.79   $18.80   $18.80  
  Purchase #3 $195.78   12.870%   $220.9769   $220.98   $221.00   $221.00  
  Purchase #4 $79.40   11.826%   $88.7898   $88.79   $88.80   $88.80  
  Purchase #5 $32.59   4.383%   $34.0184   $34.02   $34.00   $34.00  
  Purchase #6 $160.40   11.135%   $178.2605   $178.26   $178.25   $178.30  
  Purchase #7 $238.87   4.455%   $249.5117   $249.51   $249.50   $249.50  
  7 purchase totals = $877.10       $960.8574   $960.86   $960.85   $960.90