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	$137.58	13.778%	$156.5358	$156.54	$156.55	$156.50
Purchase #2	$175.33	11.470%	$195.4404	$195.44	$195.45	$195.40
Purchase #3	$169.73	12.797%	$191.4503	$191.45	$191.45	$191.50
Purchase #4	$43.44	8.137%	$46.9747	$46.97	$46.95	$47.00
Purchase #5	$174.91	12.570%	$196.8962	$196.90	$196.90	$196.90
Purchase #6	$32.29	7.236%	$34.6265	$34.63	$34.65	$34.60
Purchase #7	$59.92	12.482%	$67.3992	$67.40	$67.40	$67.40
7 purchase totals =	$793.20		$889.3231	$889.33	$889.35	$889.30