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 $147.87   10.637%   $163.5989   $163.60   $163.60   $163.60  
  Purchase #2 $248.81   3.423%   $257.3268   $257.33   $257.35   $257.30  
  Purchase #3 $214.30   4.254%   $223.4163   $223.42   $223.40   $223.40  
  Purchase #4 $55.69   7.382%   $59.801   $59.80   $59.80   $59.80  
  Purchase #5 $242.37   4.764%   $253.9165   $253.92   $253.90   $253.90  
  Purchase #6 $110.49   7.769%   $119.074   $119.07   $119.05   $119.10  
  Purchase #7 $155.67   7.617%   $167.5274   $167.53   $167.55   $167.50  
  7 purchase totals = $1,175.20       $1,244.6609   $1,244.67   $1,244.65   $1,244.60