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	$95.38	4.581%	$99.7494	$99.75	$99.75	$99.70
Purchase #2	$173.45	13.400%	$196.6923	$196.69	$196.70	$196.70
Purchase #3	$91.52	8.208%	$99.032	$99.03	$99.05	$99.00
Purchase #4	$32.43	8.231%	$35.0993	$35.10	$35.10	$35.10
Purchase #5	$115.95	10.507%	$128.1329	$128.13	$128.15	$128.10
Purchase #6	$37.40	9.366%	$40.9029	$40.90	$40.90	$40.90
Purchase #7	$243.32	10.268%	$268.3041	$268.30	$268.30	$268.30
7 purchase totals =	$789.45		$867.9129	$867.90	$867.95	$867.80