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	$217.50	3.596%	$225.3213	$225.32	$225.30	$225.30
Purchase #2	$249.74	5.785%	$264.1875	$264.19	$264.20	$264.20
Purchase #3	$82.40	9.130%	$89.9231	$89.92	$89.90	$89.90
Purchase #4	$27.36	7.140%	$29.3135	$29.31	$29.30	$29.30
Purchase #5	$172.80	10.328%	$190.6468	$190.65	$190.65	$190.60
Purchase #6	$152.30	11.539%	$169.8739	$169.87	$169.85	$169.90
Purchase #7	$46.71	6.259%	$49.6336	$49.63	$49.65	$49.60
7 purchase totals =	$948.81		$1,018.8997	$1,018.89	$1,018.85	$1,018.80