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 $152.25   5.716%   $160.9526   $160.95   $160.95   $161.00  
  Purchase #2 $233.82   10.110%   $257.4592   $257.46   $257.45   $257.50  
  Purchase #3 $177.32   8.390%   $192.1971   $192.20   $192.20   $192.20  
  Purchase #4 $173.42   13.141%   $196.2091   $196.21   $196.20   $196.20  
  Purchase #5 $39.34   9.667%   $43.143   $43.14   $43.15   $43.10  
  Purchase #6 $124.58   10.648%   $137.8453   $137.85   $137.85   $137.80  
  Purchase #7 $237.80   7.262%   $255.069   $255.07   $255.05   $255.10  
  7 purchase totals = $1,138.53       $1,242.8753   $1,242.88   $1,242.85   $1,242.90