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	$91.44	11.423%	$101.8852	$101.89	$101.90	$101.90
Purchase #2	$42.91	10.127%	$47.2555	$47.26	$47.25	$47.30
Purchase #3	$222.80	5.679%	$235.4528	$235.45	$235.45	$235.50
Purchase #4	$97.90	11.639%	$109.2946	$109.29	$109.30	$109.30
Purchase #5	$208.36	11.283%	$231.8693	$231.87	$231.85	$231.90
Purchase #6	$173.92	6.406%	$185.0613	$185.06	$185.05	$185.10
Purchase #7	$172.87	3.481%	$178.8876	$178.89	$178.90	$178.90
7 purchase totals =	$1,010.20		$1,089.7063	$1,089.71	$1,089.70	$1,089.90