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	$250.60	12.489%	$281.8974	$281.90	$281.90	$281.90
Purchase #2	$160.54	4.237%	$167.3421	$167.34	$167.35	$167.30
Purchase #3	$237.70	10.171%	$261.8765	$261.88	$261.90	$261.90
Purchase #4	$95.46	4.731%	$99.9762	$99.98	$100.00	$100.00
Purchase #5	$220.33	13.678%	$250.4667	$250.47	$250.45	$250.50
Purchase #6	$214.89	4.468%	$224.4913	$224.49	$224.50	$224.50
Purchase #7	$194.63	11.115%	$216.2631	$216.26	$216.25	$216.30
7 purchase totals =	$1,374.15		$1,502.3133	$1,502.32	$1,502.35	$1,502.40