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 $183.62   9.703%   $201.4366   $201.44   $201.45   $201.40  
  Purchase #2 $171.47   11.585%   $191.3348   $191.33   $191.35   $191.30  
  Purchase #3 $14.56   7.595%   $15.6658   $15.67   $15.65   $15.70  
  Purchase #4 $244.74   11.304%   $272.4054   $272.41   $272.40   $272.40  
  Purchase #5 $53.83   6.595%   $57.3801   $57.38   $57.40   $57.40  
  Purchase #6 $152.61   5.797%   $161.4568   $161.46   $161.45   $161.50  
  Purchase #7 $23.70   4.708%   $24.8158   $24.82   $24.80   $24.80  
  7 purchase totals = $844.53       $924.4953   $924.51   $924.50   $924.50