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	$167.76	6.308%	$178.3423	$178.34	$178.35	$178.30
Purchase #2	$207.32	6.437%	$220.6652	$220.67	$220.65	$220.70
Purchase #3	$125.77	4.796%	$131.8019	$131.80	$131.80	$131.80
Purchase #4	$131.82	5.225%	$138.7076	$138.71	$138.70	$138.70
Purchase #5	$174.50	12.375%	$196.0944	$196.09	$196.10	$196.10
Purchase #6	$242.57	10.108%	$267.089	$267.09	$267.10	$267.10
Purchase #7	$156.76	5.790%	$165.8364	$165.84	$165.85	$165.80
7 purchase totals =	$1,206.50		$1,298.5368	$1,298.54	$1,298.55	$1,298.50