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	$69.56	12.409%	$78.1917	$78.19	$78.20	$78.20
Purchase #2	$56.81	4.471%	$59.35	$59.35	$59.35	$59.40
Purchase #3	$33.38	12.808%	$37.6553	$37.66	$37.65	$37.70
Purchase #4	$197.90	13.362%	$224.3434	$224.34	$224.35	$224.30
Purchase #5	$71.32	11.715%	$79.6751	$79.68	$79.70	$79.70
Purchase #6	$213.29	13.795%	$242.7134	$242.71	$242.70	$242.70
Purchase #7	$173.57	4.159%	$180.7888	$180.79	$180.80	$180.80
7 purchase totals =	$815.83		$902.7177	$902.72	$902.75	$902.80