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	$128.86	12.543%	$145.0229	$145.02	$145.00	$145.00
Purchase #2	$199.25	13.287%	$225.7243	$225.72	$225.70	$225.70
Purchase #3	$236.48	5.211%	$248.803	$248.80	$248.80	$248.80
Purchase #4	$45.32	3.296%	$46.8137	$46.81	$46.80	$46.80
Purchase #5	$239.78	10.376%	$264.6596	$264.66	$264.65	$264.70
Purchase #6	$28.96	11.772%	$32.3692	$32.37	$32.35	$32.40
Purchase #7	$27.74	4.140%	$28.8884	$28.89	$28.90	$28.90
7 purchase totals =	$906.39		$992.2811	$992.27	$992.20	$992.30