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	$45.46	11.560%	$50.7152	$50.72	$50.70	$50.70
Purchase #2	$245.97	9.122%	$268.4074	$268.41	$268.40	$268.40
Purchase #3	$111.35	11.785%	$124.4726	$124.47	$124.45	$124.50
Purchase #4	$26.32	7.606%	$28.3219	$28.32	$28.30	$28.30
Purchase #5	$13.51	11.192%	$15.022	$15.02	$15.00	$15.00
Purchase #6	$48.82	13.456%	$55.3892	$55.39	$55.40	$55.40
Purchase #7	$139.75	11.628%	$156.0001	$156.00	$156.00	$156.00
7 purchase totals =	$631.18		$698.3284	$698.33	$698.25	$698.30