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	$77.28	8.335%	$83.7213	$83.72	$83.70	$83.70
Purchase #2	$123.66	6.654%	$131.8883	$131.89	$131.90	$131.90
Purchase #3	$48.46	12.346%	$54.4429	$54.44	$54.45	$54.40
Purchase #4	$136.69	8.824%	$148.7515	$148.75	$148.75	$148.80
Purchase #5	$78.38	9.590%	$85.8966	$85.90	$85.90	$85.90
Purchase #6	$200.44	6.355%	$213.178	$213.18	$213.20	$213.20
Purchase #7	$88.67	4.170%	$92.3675	$92.37	$92.35	$92.40
7 purchase totals =	$753.58		$810.2461	$810.25	$810.25	$810.30