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	$234.89	4.223%	$244.8094	$244.81	$244.80	$244.80
Purchase #2	$218.28	6.205%	$231.8243	$231.82	$231.80	$231.80
Purchase #3	$7.63	6.293%	$8.1102	$8.11	$8.10	$8.10
Purchase #4	$185.77	13.361%	$210.5907	$210.59	$210.60	$210.60
Purchase #5	$58.94	10.309%	$65.0161	$65.02	$65.00	$65.00
Purchase #6	$154.60	11.666%	$172.6356	$172.64	$172.65	$172.60
Purchase #7	$141.72	12.179%	$158.9801	$158.98	$159.00	$159.00
7 purchase totals =	$1,001.83		$1,091.9664	$1,091.97	$1,091.95	$1,091.90