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 $169.76   11.205%   $188.7816   $188.78   $188.80   $188.80  
  Purchase #2 $218.35   10.285%   $240.8073   $240.81   $240.80   $240.80  
  Purchase #3 $100.53   13.689%   $114.2916   $114.29   $114.30   $114.30  
  Purchase #4 $40.36   12.514%   $45.4107   $45.41   $45.40   $45.40  
  Purchase #5 $23.89   5.704%   $25.2527   $25.25   $25.25   $25.30  
  Purchase #6 $215.68   4.225%   $224.7925   $224.79   $224.80   $224.80  
  Purchase #7 $159.75   9.765%   $175.3496   $175.35   $175.35   $175.30  
  7 purchase totals = $928.32       $1,014.6860   $1,014.68   $1,014.70   $1,014.70