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	$233.60	7.423%	$250.9401	$250.94	$250.95	$250.90
Purchase #2	$60.72	11.589%	$67.7568	$67.76	$67.75	$67.80
Purchase #3	$58.49	12.109%	$65.5726	$65.57	$65.55	$65.60
Purchase #4	$78.35	8.515%	$85.0215	$85.02	$85.00	$85.00
Purchase #5	$40.37	4.408%	$42.1495	$42.15	$42.15	$42.10
Purchase #6	$216.76	13.810%	$246.6946	$246.69	$246.70	$246.70
Purchase #7	$37.38	13.700%	$42.5011	$42.50	$42.50	$42.50
7 purchase totals =	$725.67		$800.6362	$800.63	$800.60	$800.60