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	$243.44	6.473%	$259.1979	$259.20	$259.20	$259.20
Purchase #2	$66.36	12.623%	$74.7366	$74.74	$74.75	$74.70
Purchase #3	$228.50	6.670%	$243.741	$243.74	$243.75	$243.70
Purchase #4	$248.33	5.656%	$262.3755	$262.38	$262.40	$262.40
Purchase #5	$61.32	6.517%	$65.3162	$65.32	$65.30	$65.30
Purchase #6	$85.67	4.862%	$89.8353	$89.84	$89.85	$89.80
Purchase #7	$7.61	11.109%	$8.4554	$8.46	$8.45	$8.50
7 purchase totals =	$941.23		$1,003.6579	$1,003.68	$1,003.70	$1,003.60