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	$100.65	11.787%	$112.5136	$112.51	$112.50	$112.50
Purchase #2	$246.48	7.233%	$264.3079	$264.31	$264.30	$264.30
Purchase #3	$123.28	11.485%	$137.4387	$137.44	$137.45	$137.40
Purchase #4	$176.58	9.551%	$193.4452	$193.45	$193.45	$193.40
Purchase #5	$71.55	9.354%	$78.2428	$78.24	$78.25	$78.20
Purchase #6	$141.42	12.679%	$159.3506	$159.35	$159.35	$159.40
Purchase #7	$147.82	11.287%	$164.5044	$164.50	$164.50	$164.50
7 purchase totals =	$1,007.78		$1,109.8032	$1,109.80	$1,109.80	$1,109.70