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	$199.73	6.694%	$213.0999	$213.10	$213.10	$213.10
Purchase #2	$158.42	8.767%	$172.3087	$172.31	$172.30	$172.30
Purchase #3	$84.92	5.828%	$89.8691	$89.87	$89.85	$89.90
Purchase #4	$31.45	9.780%	$34.5258	$34.53	$34.55	$34.50
Purchase #5	$85.35	5.343%	$89.9103	$89.91	$89.90	$89.90
Purchase #6	$68.61	9.720%	$75.2789	$75.28	$75.30	$75.30
Purchase #7	$156.32	7.437%	$167.9455	$167.95	$167.95	$167.90
7 purchase totals =	$784.80		$842.9382	$842.95	$842.95	$842.90