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	$91.85	12.318%	$103.1641	$103.16	$103.15	$103.20
Purchase #2	$117.86	7.675%	$126.9058	$126.91	$126.90	$126.90
Purchase #3	$38.97	3.671%	$40.4006	$40.40	$40.40	$40.40
Purchase #4	$51.84	7.592%	$55.7757	$55.78	$55.80	$55.80
Purchase #5	$120.63	9.710%	$132.3432	$132.34	$132.35	$132.30
Purchase #6	$154.80	7.134%	$165.8434	$165.84	$165.85	$165.80
Purchase #7	$65.44	9.871%	$71.8996	$71.90	$71.90	$71.90
7 purchase totals =	$641.39		$696.3324	$696.33	$696.35	$696.30