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	$43.52	7.623%	$46.8375	$46.84	$46.85	$46.80
Purchase #2	$38.72	12.163%	$43.4295	$43.43	$43.45	$43.40
Purchase #3	$120.33	7.110%	$128.8855	$128.89	$128.90	$128.90
Purchase #4	$238.61	4.811%	$250.0895	$250.09	$250.10	$250.10
Purchase #5	$66.43	8.579%	$72.129	$72.13	$72.15	$72.10
Purchase #6	$97.57	11.841%	$109.1233	$109.12	$109.10	$109.10
Purchase #7	$183.67	12.263%	$206.1935	$206.19	$206.20	$206.20
7 purchase totals =	$788.85		$856.6878	$856.69	$856.75	$856.60