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	$67.82	6.731%	$72.385	$72.39	$72.40	$72.40
Purchase #2	$221.83	13.729%	$252.285	$252.29	$252.30	$252.30
Purchase #3	$99.68	11.673%	$111.3156	$111.32	$111.30	$111.30
Purchase #4	$194.64	9.458%	$213.0491	$213.05	$213.05	$213.00
Purchase #5	$133.33	3.426%	$137.8979	$137.90	$137.90	$137.90
Purchase #6	$6.56	10.663%	$7.2595	$7.26	$7.25	$7.30
Purchase #7	$130.90	8.434%	$141.9401	$141.94	$141.95	$141.90
7 purchase totals =	$854.76		$936.1322	$936.15	$936.15	$936.10