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 $243.65   9.110%   $265.8465   $265.85   $265.85   $265.80  
  Purchase #2 $247.43   9.597%   $271.1759   $271.18   $271.20   $271.20  
  Purchase #3 $67.80   12.839%   $76.5048   $76.50   $76.50   $76.50  
  Purchase #4 $216.72   11.295%   $241.1985   $241.20   $241.20   $241.20  
  Purchase #5 $10.63   3.864%   $11.0407   $11.04   $11.05   $11.00  
  Purchase #6 $213.95   5.491%   $225.698   $225.70   $225.70   $225.70  
  Purchase #7 $115.74   13.619%   $131.5026   $131.50   $131.50   $131.50  
  7 purchase totals = $1,115.92       $1,222.9670   $1,222.97   $1,223.00   $1,222.90