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	$106.40	10.460%	$117.5294	$117.53	$117.55	$117.50
Purchase #2	$141.33	7.581%	$152.0442	$152.04	$152.05	$152.00
Purchase #3	$22.93	7.638%	$24.6814	$24.68	$24.70	$24.70
Purchase #4	$41.74	6.334%	$44.3838	$44.38	$44.40	$44.40
Purchase #5	$131.30	6.500%	$139.8345	$139.83	$139.85	$139.80
Purchase #6	$30.71	7.398%	$32.9819	$32.98	$33.00	$33.00
Purchase #7	$149.38	4.775%	$156.5129	$156.51	$156.50	$156.50
7 purchase totals =	$623.79		$667.9681	$667.95	$668.05	$667.90