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	$68.30	4.269%	$71.2157	$71.22	$71.20	$71.20
Purchase #2	$74.38	8.285%	$80.5424	$80.54	$80.55	$80.50
Purchase #3	$94.46	4.806%	$98.9997	$99.00	$99.00	$99.00
Purchase #4	$88.51	12.719%	$99.7676	$99.77	$99.75	$99.80
Purchase #5	$141.34	11.425%	$157.4881	$157.49	$157.50	$157.50
Purchase #6	$246.66	11.804%	$275.7757	$275.78	$275.80	$275.80
Purchase #7	$85.87	3.767%	$89.1047	$89.10	$89.10	$89.10
7 purchase totals =	$799.52		$872.8939	$872.90	$872.90	$872.90