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 $161.65   5.821%   $171.0596   $171.06   $171.05   $171.10  
  Purchase #2 $94.41   3.112%   $97.348   $97.35   $97.35   $97.30  
  Purchase #3 $171.57   10.154%   $188.9912   $188.99   $189.00   $189.00  
  Purchase #4 $93.74   4.863%   $98.2986   $98.30   $98.30   $98.30  
  Purchase #5 $169.27   9.411%   $185.2   $185.20   $185.20   $185.20  
  Purchase #6 $210.49   12.750%   $237.3275   $237.33   $237.35   $237.30  
  Purchase #7 $91.95   3.185%   $94.8786   $94.88   $94.90   $94.90  
  7 purchase totals = $993.08       $1,073.1035   $1,073.11   $1,073.15   $1,073.10