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 $26.41   6.258%   $28.0627   $28.06   $28.05   $28.10  
  Purchase #2 $159.53   4.367%   $166.4967   $166.50   $166.50   $166.50  
  Purchase #3 $147.50   4.788%   $154.5623   $154.56   $154.55   $154.60  
  Purchase #4 $232.80   5.786%   $246.2698   $246.27   $246.25   $246.30  
  Purchase #5 $152.57   12.863%   $172.1951   $172.20   $172.20   $172.20  
  Purchase #6 $97.25   9.516%   $106.5043   $106.50   $106.50   $106.50  
  Purchase #7 $225.55   12.669%   $254.1249   $254.12   $254.10   $254.10  
  7 purchase totals = $1,041.61       $1,128.2158   $1,128.21   $1,128.15   $1,128.30