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	$41.51	3.419%	$42.9292	$42.93	$42.95	$42.90
Purchase #2	$138.70	5.499%	$146.3271	$146.33	$146.35	$146.30
Purchase #3	$48.39	6.814%	$51.6873	$51.69	$51.70	$51.70
Purchase #4	$67.43	5.770%	$71.3207	$71.32	$71.30	$71.30
Purchase #5	$203.94	9.743%	$223.8099	$223.81	$223.80	$223.80
Purchase #6	$19.55	5.397%	$20.6051	$20.61	$20.60	$20.60
Purchase #7	$59.78	5.237%	$62.9107	$62.91	$62.90	$62.90
7 purchase totals =	$579.30		$619.5900	$619.60	$619.60	$619.50