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	$56.90	7.618%	$61.2346	$61.23	$61.25	$61.20
Purchase #2	$122.26	3.501%	$126.5403	$126.54	$126.55	$126.50
Purchase #3	$151.75	7.355%	$162.9112	$162.91	$162.90	$162.90
Purchase #4	$235.74	7.486%	$253.3875	$253.39	$253.40	$253.40
Purchase #5	$68.81	7.442%	$73.9308	$73.93	$73.95	$73.90
Purchase #6	$39.31	8.345%	$42.5904	$42.59	$42.60	$42.60
Purchase #7	$123.39	3.797%	$128.0751	$128.08	$128.10	$128.10
7 purchase totals =	$798.16		$848.6699	$848.67	$848.75	$848.60