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	$59.98	12.548%	$67.5063	$67.51	$67.50	$67.50
Purchase #2	$168.52	6.251%	$179.0542	$179.05	$179.05	$179.10
Purchase #3	$6.39	8.576%	$6.938	$6.94	$6.95	$6.90
Purchase #4	$74.29	11.231%	$82.6335	$82.63	$82.65	$82.60
Purchase #5	$156.73	13.640%	$178.108	$178.11	$178.10	$178.10
Purchase #6	$139.91	11.334%	$155.7674	$155.77	$155.75	$155.80
Purchase #7	$178.54	6.827%	$190.7289	$190.73	$190.75	$190.70
7 purchase totals =	$784.36		$860.7363	$860.74	$860.75	$860.70