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	$175.46	9.329%	$191.8287	$191.83	$191.85	$191.80
Purchase #2	$41.74	8.836%	$45.4281	$45.43	$45.45	$45.40
Purchase #3	$80.89	11.317%	$90.0443	$90.04	$90.05	$90.00
Purchase #4	$41.68	11.507%	$46.4761	$46.48	$46.50	$46.50
Purchase #5	$113.50	9.420%	$124.1917	$124.19	$124.20	$124.20
Purchase #6	$30.84	3.621%	$31.9567	$31.96	$31.95	$32.00
Purchase #7	$96.25	5.231%	$101.2848	$101.28	$101.30	$101.30
7 purchase totals =	$580.36		$631.2104	$631.21	$631.30	$631.20