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	$170.62	10.377%	$188.3252	$188.33	$188.35	$188.30
Purchase #2	$207.76	3.728%	$215.5053	$215.51	$215.50	$215.50
Purchase #3	$158.42	4.454%	$165.476	$165.48	$165.50	$165.50
Purchase #4	$50.92	9.297%	$55.654	$55.65	$55.65	$55.70
Purchase #5	$6.96	4.706%	$7.2875	$7.29	$7.30	$7.30
Purchase #6	$36.67	3.185%	$37.8379	$37.84	$37.85	$37.80
Purchase #7	$34.32	11.717%	$38.3413	$38.34	$38.35	$38.30
7 purchase totals =	$665.67		$708.4272	$708.44	$708.50	$708.40