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 $58.31   13.651%   $66.2699   $66.27   $66.25   $66.30  
  Purchase #2 $206.87   8.477%   $224.4064   $224.41   $224.40   $224.40  
  Purchase #3 $40.72   13.849%   $46.3593   $46.36   $46.35   $46.40  
  Purchase #4 $166.84   13.694%   $189.6871   $189.69   $189.70   $189.70  
  Purchase #5 $186.75   5.749%   $197.4863   $197.49   $197.50   $197.50  
  Purchase #6 $88.62   8.327%   $95.9994   $96.00   $96.00   $96.00  
  Purchase #7 $250.65   4.840%   $262.7815   $262.78   $262.80   $262.80  
  7 purchase totals = $998.76       $1,082.9899   $1,083.00   $1,083.00   $1,083.10