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	$128.45	9.201%	$140.2687	$140.27	$140.25	$140.30
Purchase #2	$204.46	9.832%	$224.5625	$224.56	$224.55	$224.60
Purchase #3	$83.67	7.831%	$90.2222	$90.22	$90.20	$90.20
Purchase #4	$72.44	11.193%	$80.5482	$80.55	$80.55	$80.50
Purchase #5	$147.65	11.193%	$164.1765	$164.18	$164.20	$164.20
Purchase #6	$100.94	4.303%	$105.2834	$105.28	$105.30	$105.30
Purchase #7	$159.28	7.766%	$171.6497	$171.65	$171.65	$171.60
7 purchase totals =	$896.89		$976.7112	$976.71	$976.70	$976.70