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	$92.33	10.239%	$101.7837	$101.78	$101.80	$101.80
Purchase #2	$38.48	10.178%	$42.3965	$42.40	$42.40	$42.40
Purchase #3	$130.37	5.182%	$137.1258	$137.13	$137.15	$137.10
Purchase #4	$84.78	6.432%	$90.233	$90.23	$90.25	$90.20
Purchase #5	$7.57	4.604%	$7.9185	$7.92	$7.90	$7.90
Purchase #6	$55.72	8.275%	$60.3308	$60.33	$60.35	$60.30
Purchase #7	$221.54	13.151%	$250.6747	$250.67	$250.65	$250.70
7 purchase totals =	$630.79		$690.4630	$690.46	$690.50	$690.40