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 $240.68   9.307%   $263.0801   $263.08   $263.10   $263.10  
  Purchase #2 $192.91   6.775%   $205.9797   $205.98   $206.00   $206.00  
  Purchase #3 $86.63   9.847%   $95.1605   $95.16   $95.15   $95.20  
  Purchase #4 $63.49   7.632%   $68.3356   $68.34   $68.35   $68.30  
  Purchase #5 $111.87   9.630%   $122.6431   $122.64   $122.65   $122.60  
  Purchase #6 $46.79   8.352%   $50.6979   $50.70   $50.70   $50.70  
  Purchase #7 $7.78   7.427%   $8.3578   $8.36   $8.35   $8.40  
  7 purchase totals = $750.15       $814.2547   $814.26   $814.30   $814.30