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 $154.92   8.184%   $167.5987   $167.60   $167.60   $167.60  
  Purchase #2 $215.68   8.179%   $233.3205   $233.32   $233.30   $233.30  
  Purchase #3 $15.93   8.584%   $17.2974   $17.30   $17.30   $17.30  
  Purchase #4 $152.61   4.528%   $159.5202   $159.52   $159.50   $159.50  
  Purchase #5 $188.31   5.292%   $198.2754   $198.28   $198.30   $198.30  
  Purchase #6 $225.64   6.723%   $240.8098   $240.81   $240.80   $240.80  
  Purchase #7 $160.81   8.332%   $174.2087   $174.21   $174.20   $174.20  
  7 purchase totals = $1,113.90       $1,191.0307   $1,191.04   $1,191.00   $1,191.00