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	$31.33	6.430%	$33.3445	$33.34	$33.35	$33.30
Purchase #2	$91.78	11.497%	$102.3319	$102.33	$102.35	$102.30
Purchase #3	$38.98	4.478%	$40.7255	$40.73	$40.75	$40.70
Purchase #4	$54.50	8.868%	$59.3331	$59.33	$59.35	$59.30
Purchase #5	$136.75	12.777%	$154.2225	$154.22	$154.20	$154.20
Purchase #6	$56.26	3.647%	$58.3118	$58.31	$58.30	$58.30
Purchase #7	$137.60	4.693%	$144.0576	$144.06	$144.05	$144.10
7 purchase totals =	$547.20		$592.3269	$592.32	$592.35	$592.20