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	$20.75	4.157%	$21.6126	$21.61	$21.60	$21.60
Purchase #2	$105.57	3.547%	$109.3146	$109.31	$109.30	$109.30
Purchase #3	$81.54	7.107%	$87.335	$87.34	$87.35	$87.30
Purchase #4	$205.42	11.790%	$229.639	$229.64	$229.65	$229.60
Purchase #5	$67.93	7.278%	$72.8739	$72.87	$72.85	$72.90
Purchase #6	$166.44	7.450%	$178.8398	$178.84	$178.85	$178.80
Purchase #7	$39.71	6.112%	$42.1371	$42.14	$42.15	$42.10
7 purchase totals =	$687.36		$741.7520	$741.75	$741.75	$741.60