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 $247.29   6.570%   $263.537   $263.54   $263.55   $263.50  
  Purchase #2 $159.68   4.354%   $166.6325   $166.63   $166.65   $166.60  
  Purchase #3 $111.37   10.293%   $122.8333   $122.83   $122.85   $122.80  
  Purchase #4 $125.73   4.576%   $131.4834   $131.48   $131.50   $131.50  
  Purchase #5 $192.41   12.122%   $215.7339   $215.73   $215.75   $215.70  
  Purchase #6 $87.63   12.579%   $98.653   $98.65   $98.65   $98.70  
  Purchase #7 $174.54   4.576%   $182.527   $182.53   $182.55   $182.50  
  7 purchase totals = $1,098.65       $1,181.4001   $1,181.39   $1,181.50   $1,181.30