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 $237.60   10.437%   $262.3983   $262.40   $262.40   $262.40  
  Purchase #2 $219.77   12.464%   $247.1621   $247.16   $247.15   $247.20  
  Purchase #3 $33.34   6.761%   $35.5941   $35.59   $35.60   $35.60  
  Purchase #4 $145.88   11.532%   $162.7029   $162.70   $162.70   $162.70  
  Purchase #5 $122.29   9.745%   $134.2072   $134.21   $134.20   $134.20  
  Purchase #6 $241.30   10.155%   $265.804   $265.80   $265.80   $265.80  
  Purchase #7 $32.87   9.626%   $36.0341   $36.03   $36.05   $36.00  
  7 purchase totals = $1,033.05       $1,143.9027   $1,143.89   $1,143.90   $1,143.90