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	$39.34	9.637%	$43.1312	$43.13	$43.15	$43.10
Purchase #2	$30.75	8.544%	$33.3773	$33.38	$33.40	$33.40
Purchase #3	$100.45	10.282%	$110.7783	$110.78	$110.80	$110.80
Purchase #4	$122.41	7.368%	$131.4292	$131.43	$131.45	$131.40
Purchase #5	$79.69	3.372%	$82.3771	$82.38	$82.40	$82.40
Purchase #6	$58.49	6.800%	$62.4673	$62.47	$62.45	$62.50
Purchase #7	$216.54	10.367%	$238.9887	$238.99	$239.00	$239.00
7 purchase totals =	$647.67		$702.5491	$702.56	$702.65	$702.60