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 $202.89   8.726%   $220.5942   $220.59   $220.60   $220.60  
  Purchase #2 $199.30   4.536%   $208.3402   $208.34   $208.35   $208.30  
  Purchase #3 $203.78   13.544%   $231.38   $231.38   $231.40   $231.40  
  Purchase #4 $201.59   13.216%   $228.2321   $228.23   $228.25   $228.20  
  Purchase #5 $110.89   7.674%   $119.3997   $119.40   $119.40   $119.40  
  Purchase #6 $229.90   10.445%   $253.9131   $253.91   $253.90   $253.90  
  Purchase #7 $73.60   10.823%   $81.5657   $81.57   $81.55   $81.60  
  7 purchase totals = $1,221.95       $1,343.4250   $1,343.42   $1,343.45   $1,343.40