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	$97.72	7.529%	$105.0773	$105.08	$105.10	$105.10
Purchase #2	$229.77	11.250%	$255.6191	$255.62	$255.60	$255.60
Purchase #3	$46.31	10.633%	$51.2341	$51.23	$51.25	$51.20
Purchase #4	$82.84	12.770%	$93.4187	$93.42	$93.40	$93.40
Purchase #5	$223.83	8.782%	$243.4868	$243.49	$243.50	$243.50
Purchase #6	$22.94	12.697%	$25.8527	$25.85	$25.85	$25.90
Purchase #7	$113.59	5.133%	$119.4206	$119.42	$119.40	$119.40
7 purchase totals =	$817.00		$894.1093	$894.11	$894.10	$894.10