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	$140.60	11.393%	$156.6186	$156.62	$156.60	$156.60
Purchase #2	$188.74	5.538%	$199.1924	$199.19	$199.20	$199.20
Purchase #3	$149.28	10.299%	$164.6543	$164.65	$164.65	$164.70
Purchase #4	$79.66	10.711%	$88.1924	$88.19	$88.20	$88.20
Purchase #5	$114.62	12.352%	$128.7779	$128.78	$128.80	$128.80
Purchase #6	$40.78	4.384%	$42.5678	$42.57	$42.55	$42.60
Purchase #7	$175.91	11.668%	$196.4352	$196.44	$196.45	$196.40
7 purchase totals =	$889.59		$976.4386	$976.44	$976.45	$976.50