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	$137.50	4.746%	$144.0258	$144.03	$144.05	$144.00
Purchase #2	$53.75	3.297%	$55.5221	$55.52	$55.50	$55.50
Purchase #3	$52.30	7.306%	$56.121	$56.12	$56.10	$56.10
Purchase #4	$94.98	9.301%	$103.8141	$103.81	$103.80	$103.80
Purchase #5	$119.49	13.498%	$135.6188	$135.62	$135.60	$135.60
Purchase #6	$220.59	6.288%	$234.4607	$234.46	$234.45	$234.50
Purchase #7	$55.69	7.546%	$59.8924	$59.89	$59.90	$59.90
7 purchase totals =	$734.30		$789.4549	$789.45	$789.40	$789.40