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 $142.94   12.164%   $160.3272   $160.33   $160.35   $160.30  
  Purchase #2 $196.60   8.144%   $212.6111   $212.61   $212.60   $212.60  
  Purchase #3 $205.41   13.386%   $232.9062   $232.91   $232.90   $232.90  
  Purchase #4 $153.57   5.223%   $161.591   $161.59   $161.60   $161.60  
  Purchase #5 $51.87   6.411%   $55.1954   $55.20   $55.20   $55.20  
  Purchase #6 $161.96   12.451%   $182.1256   $182.13   $182.15   $182.10  
  Purchase #7 $159.50   4.851%   $167.2373   $167.24   $167.25   $167.20  
  7 purchase totals = $1,071.85       $1,171.9938   $1,172.01   $1,172.05   $1,171.90