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	$11.98	9.721%	$13.1446	$13.14	$13.15	$13.10
Purchase #2	$196.34	13.401%	$222.6515	$222.65	$222.65	$222.70
Purchase #3	$116.88	10.136%	$128.727	$128.73	$128.75	$128.70
Purchase #4	$250.39	6.428%	$266.4851	$266.49	$266.50	$266.50
Purchase #5	$88.36	12.245%	$99.1797	$99.18	$99.20	$99.20
Purchase #6	$71.44	9.121%	$77.956	$77.96	$77.95	$78.00
Purchase #7	$117.83	11.431%	$131.2991	$131.30	$131.30	$131.30
7 purchase totals =	$853.22		$939.4430	$939.45	$939.50	$939.50