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	$14.75	7.820%	$15.9035	$15.90	$15.90	$15.90
Purchase #2	$227.57	11.308%	$253.3036	$253.30	$253.30	$253.30
Purchase #3	$236.66	11.542%	$263.9753	$263.98	$264.00	$264.00
Purchase #4	$7.70	12.454%	$8.659	$8.66	$8.65	$8.70
Purchase #5	$187.64	4.620%	$196.309	$196.31	$196.30	$196.30
Purchase #6	$171.77	4.559%	$179.601	$179.60	$179.60	$179.60
Purchase #7	$208.70	4.865%	$218.8533	$218.85	$218.85	$218.90
7 purchase totals =	$1,054.79		$1,136.6047	$1,136.60	$1,136.60	$1,136.70