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	$183.95	12.225%	$206.4379	$206.44	$206.45	$206.40
Purchase #2	$140.72	4.388%	$146.8948	$146.89	$146.90	$146.90
Purchase #3	$130.63	8.373%	$141.5676	$141.57	$141.55	$141.60
Purchase #4	$22.56	6.423%	$24.009	$24.01	$24.00	$24.00
Purchase #5	$90.43	9.873%	$99.3582	$99.36	$99.35	$99.40
Purchase #6	$129.68	4.497%	$135.5117	$135.51	$135.50	$135.50
Purchase #7	$37.75	13.803%	$42.9606	$42.96	$42.95	$43.00
7 purchase totals =	$735.72		$796.7398	$796.74	$796.70	$796.80