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	$63.49	13.195%	$71.8675	$71.87	$71.85	$71.90
Purchase #2	$55.39	6.507%	$58.9942	$58.99	$59.00	$59.00
Purchase #3	$124.75	13.676%	$141.8108	$141.81	$141.80	$141.80
Purchase #4	$100.43	13.433%	$113.9208	$113.92	$113.90	$113.90
Purchase #5	$191.92	13.291%	$217.4281	$217.43	$217.45	$217.40
Purchase #6	$148.74	9.280%	$162.5431	$162.54	$162.55	$162.50
Purchase #7	$37.86	6.115%	$40.1751	$40.18	$40.20	$40.20
7 purchase totals =	$722.58		$806.7396	$806.74	$806.75	$806.70