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	$98.81	7.196%	$105.9204	$105.92	$105.90	$105.90
Purchase #2	$79.27	9.427%	$86.7428	$86.74	$86.75	$86.70
Purchase #3	$89.74	5.507%	$94.682	$94.68	$94.70	$94.70
Purchase #4	$65.38	9.242%	$71.4224	$71.42	$71.40	$71.40
Purchase #5	$35.41	12.189%	$39.7261	$39.73	$39.75	$39.70
Purchase #6	$165.79	3.670%	$171.8745	$171.87	$171.85	$171.90
Purchase #7	$60.54	11.799%	$67.6831	$67.68	$67.70	$67.70
7 purchase totals =	$594.94		$638.0513	$638.04	$638.05	$638.00