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	$239.80	9.717%	$263.1014	$263.10	$263.10	$263.10
Purchase #2	$72.89	11.240%	$81.0828	$81.08	$81.10	$81.10
Purchase #3	$72.93	13.394%	$82.6982	$82.70	$82.70	$82.70
Purchase #4	$87.96	11.436%	$98.0191	$98.02	$98.00	$98.00
Purchase #5	$122.94	6.813%	$131.3159	$131.32	$131.30	$131.30
Purchase #6	$65.65	3.240%	$67.7771	$67.78	$67.80	$67.80
Purchase #7	$159.68	7.819%	$172.1654	$172.17	$172.15	$172.20
7 purchase totals =	$821.85		$896.1599	$896.17	$896.15	$896.20