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	$215.25	13.782%	$244.9158	$244.92	$244.90	$244.90
Purchase #2	$46.41	4.262%	$48.388	$48.39	$48.40	$48.40
Purchase #3	$150.36	4.627%	$157.3172	$157.32	$157.30	$157.30
Purchase #4	$26.33	13.133%	$29.7879	$29.79	$29.80	$29.80
Purchase #5	$129.90	11.227%	$144.4839	$144.48	$144.50	$144.50
Purchase #6	$243.65	12.482%	$274.0624	$274.06	$274.05	$274.10
Purchase #7	$53.74	11.502%	$59.9212	$59.92	$59.90	$59.90
7 purchase totals =	$865.64		$958.8764	$958.88	$958.85	$958.90