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	$25.45	13.487%	$28.8824	$28.88	$28.90	$28.90
Purchase #2	$144.39	7.558%	$155.303	$155.30	$155.30	$155.30
Purchase #3	$187.72	4.645%	$196.4396	$196.44	$196.45	$196.40
Purchase #4	$130.49	9.178%	$142.4664	$142.47	$142.45	$142.50
Purchase #5	$49.48	7.699%	$53.2895	$53.29	$53.30	$53.30
Purchase #6	$158.52	5.678%	$167.5208	$167.52	$167.50	$167.50
Purchase #7	$235.40	13.800%	$267.8852	$267.89	$267.90	$267.90
7 purchase totals =	$931.45		$1,011.7869	$1,011.79	$1,011.80	$1,011.80