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	$12.38	5.792%	$13.097	$13.10	$13.10	$13.10
Purchase #2	$177.39	4.752%	$185.8196	$185.82	$185.80	$185.80
Purchase #3	$221.90	11.459%	$247.3275	$247.33	$247.35	$247.30
Purchase #4	$64.73	9.399%	$70.814	$70.81	$70.80	$70.80
Purchase #5	$140.57	8.326%	$152.2739	$152.27	$152.25	$152.30
Purchase #6	$83.92	7.578%	$90.2795	$90.28	$90.30	$90.30
Purchase #7	$191.39	6.213%	$203.2811	$203.28	$203.30	$203.30
7 purchase totals =	$892.28		$962.8926	$962.89	$962.90	$962.90