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	$155.46	6.394%	$165.4001	$165.40	$165.40	$165.40
Purchase #2	$94.98	5.304%	$100.0177	$100.02	$100.00	$100.00
Purchase #3	$102.75	3.477%	$106.3226	$106.32	$106.30	$106.30
Purchase #4	$6.78	4.679%	$7.0972	$7.10	$7.10	$7.10
Purchase #5	$67.39	5.742%	$71.2595	$71.26	$71.25	$71.30
Purchase #6	$159.46	12.575%	$179.5121	$179.51	$179.50	$179.50
Purchase #7	$115.69	6.201%	$122.8639	$122.86	$122.85	$122.90
7 purchase totals =	$702.51		$752.4731	$752.47	$752.40	$752.50