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	$35.61	3.403%	$36.8218	$36.82	$36.80	$36.80
Purchase #2	$107.47	8.426%	$116.5254	$116.53	$116.55	$116.50
Purchase #3	$106.39	11.266%	$118.3759	$118.38	$118.40	$118.40
Purchase #4	$179.39	3.442%	$185.5646	$185.56	$185.55	$185.60
Purchase #5	$52.99	11.191%	$58.9201	$58.92	$58.90	$58.90
Purchase #6	$35.94	9.579%	$39.3827	$39.38	$39.40	$39.40
Purchase #7	$91.41	10.172%	$100.7082	$100.71	$100.70	$100.70
7 purchase totals =	$609.20		$656.2987	$656.30	$656.30	$656.30