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	$122.34	13.507%	$138.8645	$138.86	$138.85	$138.90
Purchase #2	$82.96	11.484%	$92.4871	$92.49	$92.50	$92.50
Purchase #3	$85.85	12.689%	$96.7435	$96.74	$96.75	$96.70
Purchase #4	$105.56	5.520%	$111.3869	$111.39	$111.40	$111.40
Purchase #5	$43.44	11.765%	$48.5507	$48.55	$48.55	$48.60
Purchase #6	$139.75	12.464%	$157.1684	$157.17	$157.15	$157.20
Purchase #7	$101.27	11.465%	$112.8806	$112.88	$112.90	$112.90
7 purchase totals =	$681.17		$758.0817	$758.08	$758.10	$758.20