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	$231.32	7.257%	$248.1069	$248.11	$248.10	$248.10
Purchase #2	$39.50	3.585%	$40.9161	$40.92	$40.90	$40.90
Purchase #3	$39.57	13.670%	$44.9792	$44.98	$45.00	$45.00
Purchase #4	$95.33	8.584%	$103.5131	$103.51	$103.50	$103.50
Purchase #5	$88.70	11.645%	$99.0291	$99.03	$99.05	$99.00
Purchase #6	$40.77	11.133%	$45.3089	$45.31	$45.30	$45.30
Purchase #7	$160.45	4.762%	$168.0906	$168.09	$168.10	$168.10
7 purchase totals =	$695.64		$749.9439	$749.95	$749.95	$749.90