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	$98.52	12.137%	$110.4774	$110.48	$110.50	$110.50
Purchase #2	$124.44	5.576%	$131.3788	$131.38	$131.40	$131.40
Purchase #3	$183.95	11.215%	$204.58	$204.58	$204.60	$204.60
Purchase #4	$151.47	10.855%	$167.9121	$167.91	$167.90	$167.90
Purchase #5	$88.50	13.138%	$100.1271	$100.13	$100.15	$100.10
Purchase #6	$67.81	12.378%	$76.2035	$76.20	$76.20	$76.20
Purchase #7	$94.41	5.294%	$99.4081	$99.41	$99.40	$99.40
7 purchase totals =	$809.10		$890.0870	$890.09	$890.15	$890.10