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	$71.25	10.425%	$78.6778	$78.68	$78.70	$78.70
Purchase #2	$172.76	4.379%	$180.3252	$180.33	$180.35	$180.30
Purchase #3	$198.98	5.496%	$209.9159	$209.92	$209.90	$209.90
Purchase #4	$217.79	11.691%	$243.2518	$243.25	$243.25	$243.30
Purchase #5	$234.79	3.588%	$243.2143	$243.21	$243.20	$243.20
Purchase #6	$163.25	5.596%	$172.3855	$172.39	$172.40	$172.40
Purchase #7	$174.91	12.467%	$196.716	$196.72	$196.70	$196.70
7 purchase totals =	$1,233.73		$1,324.4865	$1,324.50	$1,324.50	$1,324.50