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	$99.37	3.436%	$102.7844	$102.78	$102.80	$102.80
Purchase #2	$56.93	4.192%	$59.3165	$59.32	$59.30	$59.30
Purchase #3	$135.50	4.707%	$141.878	$141.88	$141.90	$141.90
Purchase #4	$160.43	7.688%	$172.7639	$172.76	$172.75	$172.80
Purchase #5	$78.91	10.846%	$87.4686	$87.47	$87.45	$87.50
Purchase #6	$46.77	5.714%	$49.4424	$49.44	$49.45	$49.40
Purchase #7	$196.65	11.488%	$219.2412	$219.24	$219.25	$219.20
7 purchase totals =	$774.56		$832.8950	$832.89	$832.90	$832.90