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	$80.30	11.658%	$89.6614	$89.66	$89.65	$89.70
Purchase #2	$89.76	6.644%	$95.7237	$95.72	$95.70	$95.70
Purchase #3	$76.86	5.786%	$81.3071	$81.31	$81.30	$81.30
Purchase #4	$136.76	12.474%	$153.8194	$153.82	$153.80	$153.80
Purchase #5	$33.85	6.219%	$35.9551	$35.96	$35.95	$36.00
Purchase #6	$211.72	9.586%	$232.0155	$232.02	$232.00	$232.00
Purchase #7	$132.77	11.560%	$148.1182	$148.12	$148.10	$148.10
7 purchase totals =	$762.02		$836.6004	$836.61	$836.50	$836.60