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	$69.97	12.167%	$78.4832	$78.48	$78.50	$78.50
Purchase #2	$92.54	12.870%	$104.4499	$104.45	$104.45	$104.40
Purchase #3	$203.59	7.151%	$218.1487	$218.15	$218.15	$218.10
Purchase #4	$71.67	12.193%	$80.4087	$80.41	$80.40	$80.40
Purchase #5	$91.49	5.635%	$96.6455	$96.65	$96.65	$96.60
Purchase #6	$135.84	6.146%	$144.1887	$144.19	$144.20	$144.20
Purchase #7	$243.47	6.559%	$259.4392	$259.44	$259.45	$259.40
7 purchase totals =	$908.57		$981.7639	$981.77	$981.80	$981.60