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	$144.72	6.807%	$154.5711	$154.57	$154.55	$154.60
Purchase #2	$93.54	12.657%	$105.3794	$105.38	$105.40	$105.40
Purchase #3	$196.73	9.595%	$215.6062	$215.61	$215.60	$215.60
Purchase #4	$96.47	3.576%	$99.9198	$99.92	$99.90	$99.90
Purchase #5	$194.81	10.251%	$214.78	$214.78	$214.80	$214.80
Purchase #6	$188.88	5.142%	$198.5922	$198.59	$198.60	$198.60
Purchase #7	$7.95	10.731%	$8.8031	$8.80	$8.80	$8.80
7 purchase totals =	$923.10		$997.6518	$997.65	$997.65	$997.70