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	$79.68	4.785%	$83.4927	$83.49	$83.50	$83.50
Purchase #2	$223.33	7.850%	$240.8614	$240.86	$240.85	$240.90
Purchase #3	$130.50	12.122%	$146.3192	$146.32	$146.30	$146.30
Purchase #4	$105.72	12.840%	$119.2944	$119.29	$119.30	$119.30
Purchase #5	$216.63	3.615%	$224.4612	$224.46	$224.45	$224.50
Purchase #6	$130.31	9.568%	$142.7781	$142.78	$142.80	$142.80
Purchase #7	$38.33	5.452%	$40.4198	$40.42	$40.40	$40.40
7 purchase totals =	$924.50		$997.6268	$997.62	$997.60	$997.70