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	$243.64	11.777%	$272.3335	$272.33	$272.35	$272.30
Purchase #2	$72.60	8.144%	$78.5125	$78.51	$78.50	$78.50
Purchase #3	$131.88	13.215%	$149.3079	$149.31	$149.30	$149.30
Purchase #4	$229.57	4.257%	$239.3428	$239.34	$239.35	$239.30
Purchase #5	$122.48	7.429%	$131.579	$131.58	$131.60	$131.60
Purchase #6	$58.64	9.631%	$64.2876	$64.29	$64.30	$64.30
Purchase #7	$152.31	3.318%	$157.3636	$157.36	$157.35	$157.40
7 purchase totals =	$1,011.12		$1,092.7269	$1,092.72	$1,092.75	$1,092.70