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	$169.46	6.377%	$180.2665	$180.27	$180.25	$180.30
Purchase #2	$96.45	3.790%	$100.1055	$100.11	$100.10	$100.10
Purchase #3	$165.57	10.204%	$182.4648	$182.46	$182.45	$182.50
Purchase #4	$228.95	12.696%	$258.0175	$258.02	$258.00	$258.00
Purchase #5	$113.51	12.465%	$127.659	$127.66	$127.65	$127.70
Purchase #6	$199.65	5.594%	$210.8184	$210.82	$210.80	$210.80
Purchase #7	$118.71	8.418%	$128.703	$128.70	$128.70	$128.70
7 purchase totals =	$1,092.30		$1,188.0347	$1,188.04	$1,187.95	$1,188.10