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	$38.60	4.477%	$40.3281	$40.33	$40.35	$40.30
Purchase #2	$250.65	9.813%	$275.2463	$275.25	$275.25	$275.20
Purchase #3	$148.67	7.566%	$159.9184	$159.92	$159.90	$159.90
Purchase #4	$212.54	4.574%	$222.2616	$222.26	$222.25	$222.30
Purchase #5	$81.89	11.654%	$91.4335	$91.43	$91.45	$91.40
Purchase #6	$40.57	7.125%	$43.4606	$43.46	$43.45	$43.50
Purchase #7	$98.73	13.134%	$111.6972	$111.70	$111.70	$111.70
7 purchase totals =	$871.65		$944.3457	$944.35	$944.35	$944.30