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	$50.95	8.788%	$55.4275	$55.43	$55.45	$55.40
Purchase #2	$98.61	7.333%	$105.8411	$105.84	$105.85	$105.80
Purchase #3	$185.81	13.370%	$210.6528	$210.65	$210.65	$210.70
Purchase #4	$99.82	5.764%	$105.5736	$105.57	$105.55	$105.60
Purchase #5	$139.98	7.374%	$150.3021	$150.30	$150.30	$150.30
Purchase #6	$177.88	5.759%	$188.1241	$188.12	$188.10	$188.10
Purchase #7	$20.79	5.826%	$22.0012	$22.00	$22.00	$22.00
7 purchase totals =	$773.84		$837.9224	$837.91	$837.90	$837.90