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	$38.78	5.584%	$40.9455	$40.95	$40.95	$40.90
Purchase #2	$139.44	6.601%	$148.6444	$148.64	$148.65	$148.60
Purchase #3	$244.39	12.494%	$274.9241	$274.92	$274.90	$274.90
Purchase #4	$14.30	5.215%	$15.0457	$15.05	$15.05	$15.00
Purchase #5	$244.32	10.820%	$270.7554	$270.76	$270.75	$270.80
Purchase #6	$182.33	4.424%	$190.3963	$190.40	$190.40	$190.40
Purchase #7	$33.95	4.603%	$35.5127	$35.51	$35.50	$35.50
7 purchase totals =	$897.51		$976.2241	$976.23	$976.20	$976.10