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 $147.55   10.614%   $163.211   $163.21   $163.20   $163.20  
  Purchase #2 $87.89   9.351%   $96.1086   $96.11   $96.10   $96.10  
  Purchase #3 $180.40   6.737%   $192.5535   $192.55   $192.55   $192.60  
  Purchase #4 $249.87   7.458%   $268.5053   $268.51   $268.50   $268.50  
  Purchase #5 $223.82   9.845%   $245.8551   $245.86   $245.85   $245.90  
  Purchase #6 $71.79   13.389%   $81.402   $81.40   $81.40   $81.40  
  Purchase #7 $111.77   4.832%   $117.1707   $117.17   $117.15   $117.20  
  7 purchase totals = $1,073.09       $1,164.8062   $1,164.81   $1,164.75   $1,164.90