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	$29.86	6.589%	$31.8275	$31.83	$31.85	$31.80
Purchase #2	$65.98	11.573%	$73.6159	$73.62	$73.60	$73.60
Purchase #3	$222.73	12.373%	$250.2884	$250.29	$250.30	$250.30
Purchase #4	$118.37	10.579%	$130.8924	$130.89	$130.90	$130.90
Purchase #5	$104.82	3.305%	$108.2843	$108.28	$108.30	$108.30
Purchase #6	$83.70	6.643%	$89.2602	$89.26	$89.25	$89.30
Purchase #7	$41.79	13.764%	$47.542	$47.54	$47.55	$47.50
7 purchase totals =	$667.25		$731.7107	$731.71	$731.75	$731.70