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	$183.52	3.629%	$190.1799	$190.18	$190.20	$190.20
Purchase #2	$56.64	11.817%	$63.3331	$63.33	$63.35	$63.30
Purchase #3	$201.66	13.855%	$229.6	$229.60	$229.60	$229.60
Purchase #4	$90.54	10.301%	$99.8665	$99.87	$99.85	$99.90
Purchase #5	$210.97	4.515%	$220.4953	$220.50	$220.50	$220.50
Purchase #6	$141.71	11.290%	$157.7091	$157.71	$157.70	$157.70
Purchase #7	$129.58	7.708%	$139.568	$139.57	$139.55	$139.60
7 purchase totals =	$1,014.62		$1,100.7519	$1,100.76	$1,100.75	$1,100.80