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 $198.74   3.710%   $206.1133   $206.11   $206.10   $206.10  
  Purchase #2 $130.38   6.346%   $138.6539   $138.65   $138.65   $138.70  
  Purchase #3 $44.65   8.601%   $48.4903   $48.49   $48.50   $48.50  
  Purchase #4 $86.78   13.657%   $98.6315   $98.63   $98.65   $98.60  
  Purchase #5 $146.40   6.264%   $155.5705   $155.57   $155.55   $155.60  
  Purchase #6 $145.83   11.752%   $162.9679   $162.97   $162.95   $163.00  
  Purchase #7 $110.99   4.773%   $116.2876   $116.29   $116.30   $116.30  
  7 purchase totals = $863.77       $926.7150   $926.71   $926.70   $926.80