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	$29.59	4.568%	$30.9417	$30.94	$30.95	$30.90
Purchase #2	$121.72	8.114%	$131.5964	$131.60	$131.60	$131.60
Purchase #3	$30.29	7.339%	$32.513	$32.51	$32.50	$32.50
Purchase #4	$203.93	11.694%	$227.7776	$227.78	$227.80	$227.80
Purchase #5	$137.75	10.437%	$152.127	$152.13	$152.15	$152.10
Purchase #6	$165.25	13.650%	$187.8066	$187.81	$187.80	$187.80
Purchase #7	$148.50	9.122%	$162.0462	$162.05	$162.05	$162.00
7 purchase totals =	$837.03		$924.8085	$924.82	$924.85	$924.70