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	$16.74	6.803%	$17.8788	$17.88	$17.90	$17.90
Purchase #2	$86.83	6.638%	$92.5938	$92.59	$92.60	$92.60
Purchase #3	$18.37	10.231%	$20.2494	$20.25	$20.25	$20.20
Purchase #4	$52.44	12.434%	$58.9604	$58.96	$58.95	$59.00
Purchase #5	$230.69	6.319%	$245.2673	$245.27	$245.25	$245.30
Purchase #6	$150.94	11.760%	$168.6905	$168.69	$168.70	$168.70
Purchase #7	$139.93	7.299%	$150.1435	$150.14	$150.15	$150.10
7 purchase totals =	$695.94		$753.7837	$753.78	$753.80	$753.80