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 $132.81   13.723%   $151.0355   $151.04   $151.05   $151.00  
  Purchase #2 $49.91   13.561%   $56.6783   $56.68   $56.70   $56.70  
  Purchase #3 $119.47   7.435%   $128.3526   $128.35   $128.35   $128.40  
  Purchase #4 $123.91   5.422%   $130.6284   $130.63   $130.65   $130.60  
  Purchase #5 $194.55   13.313%   $220.4504   $220.45   $220.45   $220.50  
  Purchase #6 $59.31   12.610%   $66.789   $66.79   $66.80   $66.80  
  Purchase #7 $185.96   6.679%   $198.3803   $198.38   $198.40   $198.40  
  7 purchase totals = $865.92       $952.3145   $952.32   $952.40   $952.40