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	$71.76	11.650%	$80.12	$80.12	$80.10	$80.10
Purchase #2	$236.66	8.262%	$256.2128	$256.21	$256.20	$256.20
Purchase #3	$24.28	12.387%	$27.2876	$27.29	$27.30	$27.30
Purchase #4	$247.29	4.764%	$259.0709	$259.07	$259.05	$259.10
Purchase #5	$187.82	4.874%	$196.9743	$196.97	$196.95	$197.00
Purchase #6	$213.35	13.847%	$242.8926	$242.89	$242.90	$242.90
Purchase #7	$225.90	5.703%	$238.7831	$238.78	$238.80	$238.80
7 purchase totals =	$1,207.06		$1,301.3413	$1,301.33	$1,301.30	$1,301.40