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	$221.76	8.310%	$240.1883	$240.19	$240.20	$240.20
Purchase #2	$131.67	5.460%	$138.8592	$138.86	$138.85	$138.90
Purchase #3	$89.41	11.102%	$99.3363	$99.34	$99.35	$99.30
Purchase #4	$77.87	10.854%	$86.322	$86.32	$86.30	$86.30
Purchase #5	$212.78	13.329%	$241.1414	$241.14	$241.15	$241.10
Purchase #6	$133.89	7.109%	$143.4082	$143.41	$143.40	$143.40
Purchase #7	$52.27	4.274%	$54.504	$54.50	$54.50	$54.50
7 purchase totals =	$919.65		$1,003.7594	$1,003.76	$1,003.75	$1,003.70