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	$100.50	9.431%	$109.9782	$109.98	$110.00	$110.00
Purchase #2	$152.57	3.487%	$157.8901	$157.89	$157.90	$157.90
Purchase #3	$52.81	4.565%	$55.2208	$55.22	$55.20	$55.20
Purchase #4	$51.65	7.170%	$55.3533	$55.35	$55.35	$55.40
Purchase #5	$116.73	10.214%	$128.6528	$128.65	$128.65	$128.70
Purchase #6	$67.29	8.222%	$72.8226	$72.82	$72.80	$72.80
Purchase #7	$38.78	12.852%	$43.764	$43.76	$43.75	$43.80
7 purchase totals =	$580.33		$623.6818	$623.67	$623.65	$623.80