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	$134.56	9.312%	$147.0902	$147.09	$147.10	$147.10
Purchase #2	$117.48	8.386%	$127.3319	$127.33	$127.35	$127.30
Purchase #3	$90.38	12.178%	$101.3865	$101.39	$101.40	$101.40
Purchase #4	$125.82	12.775%	$141.8935	$141.89	$141.90	$141.90
Purchase #5	$120.60	9.375%	$131.9063	$131.91	$131.90	$131.90
Purchase #6	$5.89	13.595%	$6.6907	$6.69	$6.70	$6.70
Purchase #7	$230.27	5.236%	$242.3269	$242.33	$242.35	$242.30
7 purchase totals =	$825.00		$898.6260	$898.63	$898.70	$898.60