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	$47.61	8.147%	$51.4888	$51.49	$51.50	$51.50
Purchase #2	$86.88	11.289%	$96.6879	$96.69	$96.70	$96.70
Purchase #3	$67.34	7.564%	$72.4336	$72.43	$72.45	$72.40
Purchase #4	$161.37	12.843%	$182.0947	$182.09	$182.10	$182.10
Purchase #5	$89.89	4.764%	$94.1724	$94.17	$94.15	$94.20
Purchase #6	$164.65	10.820%	$182.4651	$182.47	$182.45	$182.50
Purchase #7	$137.74	4.487%	$143.9204	$143.92	$143.90	$143.90
7 purchase totals =	$755.48		$823.2629	$823.26	$823.25	$823.30