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	$47.64	11.828%	$53.2749	$53.27	$53.25	$53.30
Purchase #2	$182.94	3.318%	$189.0099	$189.01	$189.00	$189.00
Purchase #3	$80.68	10.793%	$89.3878	$89.39	$89.40	$89.40
Purchase #4	$39.49	11.162%	$43.8979	$43.90	$43.90	$43.90
Purchase #5	$243.77	11.497%	$271.7962	$271.80	$271.80	$271.80
Purchase #6	$164.66	12.560%	$185.3413	$185.34	$185.35	$185.30
Purchase #7	$237.42	4.590%	$248.3176	$248.32	$248.30	$248.30
7 purchase totals =	$996.60		$1,081.0256	$1,081.03	$1,081.00	$1,081.00