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	$146.46	12.323%	$164.5083	$164.51	$164.50	$164.50
Purchase #2	$26.66	8.490%	$28.9234	$28.92	$28.90	$28.90
Purchase #3	$30.95	5.326%	$32.5984	$32.60	$32.60	$32.60
Purchase #4	$72.50	7.853%	$78.1934	$78.19	$78.20	$78.20
Purchase #5	$225.89	6.649%	$240.9094	$240.91	$240.90	$240.90
Purchase #6	$118.31	8.289%	$128.1167	$128.12	$128.10	$128.10
Purchase #7	$136.30	7.688%	$146.7787	$146.78	$146.80	$146.80
7 purchase totals =	$757.07		$820.0283	$820.03	$820.00	$820.00