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	$236.74	12.687%	$266.7752	$266.78	$266.80	$266.80
Purchase #2	$91.85	13.359%	$104.1202	$104.12	$104.10	$104.10
Purchase #3	$39.54	6.351%	$42.0512	$42.05	$42.05	$42.10
Purchase #4	$95.63	7.189%	$102.5048	$102.50	$102.50	$102.50
Purchase #5	$31.73	10.669%	$35.1153	$35.12	$35.10	$35.10
Purchase #6	$232.52	12.369%	$261.2804	$261.28	$261.30	$261.30
Purchase #7	$23.59	3.726%	$24.469	$24.47	$24.45	$24.50
7 purchase totals =	$751.60		$836.3161	$836.32	$836.30	$836.40