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	$129.26	6.155%	$137.216	$137.22	$137.20	$137.20
Purchase #2	$138.56	5.543%	$146.2404	$146.24	$146.25	$146.20
Purchase #3	$47.64	3.806%	$49.4532	$49.45	$49.45	$49.50
Purchase #4	$83.89	6.173%	$89.0685	$89.07	$89.05	$89.10
Purchase #5	$32.68	13.483%	$37.0862	$37.09	$37.10	$37.10
Purchase #6	$169.80	5.114%	$178.4836	$178.48	$178.50	$178.50
Purchase #7	$140.49	11.645%	$156.8501	$156.85	$156.85	$156.90
7 purchase totals =	$742.32		$794.3980	$794.40	$794.40	$794.50