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	$52.83	7.781%	$56.9407	$56.94	$56.95	$56.90
Purchase #2	$179.37	11.839%	$200.6056	$200.61	$200.60	$200.60
Purchase #3	$47.90	11.659%	$53.4847	$53.48	$53.50	$53.50
Purchase #4	$43.63	6.181%	$46.3268	$46.33	$46.35	$46.30
Purchase #5	$153.80	11.487%	$171.467	$171.47	$171.45	$171.50
Purchase #6	$42.97	5.165%	$45.1894	$45.19	$45.20	$45.20
Purchase #7	$88.74	8.282%	$96.0894	$96.09	$96.10	$96.10
7 purchase totals =	$609.24		$670.1036	$670.11	$670.15	$670.10