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	$73.41	7.359%	$78.8122	$78.81	$78.80	$78.80
Purchase #2	$114.72	11.770%	$128.2225	$128.22	$128.20	$128.20
Purchase #3	$203.82	10.379%	$224.9745	$224.97	$224.95	$225.00
Purchase #4	$33.64	9.676%	$36.895	$36.90	$36.90	$36.90
Purchase #5	$242.83	6.745%	$259.2089	$259.21	$259.20	$259.20
Purchase #6	$227.58	12.309%	$255.5928	$255.59	$255.60	$255.60
Purchase #7	$196.56	3.656%	$203.7462	$203.75	$203.75	$203.70
7 purchase totals =	$1,092.56		$1,187.4521	$1,187.45	$1,187.40	$1,187.40