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 $248.62   11.739%   $277.8055   $277.81   $277.80   $277.80  
  Purchase #2 $119.31   10.619%   $131.9795   $131.98   $132.00   $132.00  
  Purchase #3 $248.35   9.206%   $271.2131   $271.21   $271.20   $271.20  
  Purchase #4 $64.62   4.686%   $67.6481   $67.65   $67.65   $67.60  
  Purchase #5 $160.64   12.286%   $180.3762   $180.38   $180.40   $180.40  
  Purchase #6 $168.30   6.128%   $178.6134   $178.61   $178.60   $178.60  
  Purchase #7 $109.81   13.225%   $124.3324   $124.33   $124.35   $124.30  
  7 purchase totals = $1,119.65       $1,231.9682   $1,231.97   $1,232.00   $1,231.90