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	$15.65	13.478%	$17.7593	$17.76	$17.75	$17.80
Purchase #2	$189.35	5.434%	$199.6393	$199.64	$199.65	$199.60
Purchase #3	$27.38	4.533%	$28.6211	$28.62	$28.60	$28.60
Purchase #4	$233.80	13.179%	$264.6125	$264.61	$264.60	$264.60
Purchase #5	$238.74	13.752%	$271.5715	$271.57	$271.55	$271.60
Purchase #6	$161.43	6.698%	$172.2426	$172.24	$172.25	$172.20
Purchase #7	$193.25	13.787%	$219.8934	$219.89	$219.90	$219.90
7 purchase totals =	$1,059.60		$1,174.3397	$1,174.33	$1,174.30	$1,174.30