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	$33.91	12.863%	$38.2718	$38.27	$38.25	$38.30
Purchase #2	$65.78	7.763%	$70.8865	$70.89	$70.90	$70.90
Purchase #3	$66.73	6.575%	$71.1175	$71.12	$71.10	$71.10
Purchase #4	$142.90	6.397%	$152.0413	$152.04	$152.05	$152.00
Purchase #5	$190.59	10.873%	$211.3129	$211.31	$211.30	$211.30
Purchase #6	$236.71	12.848%	$267.1225	$267.12	$267.10	$267.10
Purchase #7	$128.68	4.385%	$134.3226	$134.32	$134.30	$134.30
7 purchase totals =	$865.30		$945.0751	$945.07	$945.00	$945.00