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	$39.88	6.497%	$42.471	$42.47	$42.45	$42.50
Purchase #2	$201.42	12.175%	$225.9429	$225.94	$225.95	$225.90
Purchase #3	$95.78	10.436%	$105.7756	$105.78	$105.80	$105.80
Purchase #4	$130.82	11.783%	$146.2345	$146.23	$146.25	$146.20
Purchase #5	$201.81	4.767%	$211.4303	$211.43	$211.45	$211.40
Purchase #6	$247.35	8.455%	$268.2634	$268.26	$268.25	$268.30
Purchase #7	$53.27	13.278%	$60.3432	$60.34	$60.35	$60.30
7 purchase totals =	$970.33		$1,060.4609	$1,060.45	$1,060.50	$1,060.40