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	$115.63	12.243%	$129.7866	$129.79	$129.80	$129.80
Purchase #2	$210.88	11.301%	$234.7115	$234.71	$234.70	$234.70
Purchase #3	$129.28	6.444%	$137.6108	$137.61	$137.60	$137.60
Purchase #4	$80.33	4.353%	$83.8268	$83.83	$83.85	$83.80
Purchase #5	$188.75	11.304%	$210.0863	$210.09	$210.10	$210.10
Purchase #6	$222.98	3.425%	$230.6171	$230.62	$230.60	$230.60
Purchase #7	$78.56	8.319%	$85.0954	$85.10	$85.10	$85.10
7 purchase totals =	$1,026.41		$1,111.7345	$1,111.75	$1,111.75	$1,111.70