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	$128.44	12.368%	$144.3255	$144.33	$144.35	$144.30
Purchase #2	$186.96	12.682%	$210.6703	$210.67	$210.65	$210.70
Purchase #3	$168.91	6.840%	$180.4634	$180.46	$180.45	$180.50
Purchase #4	$190.94	12.561%	$214.924	$214.92	$214.90	$214.90
Purchase #5	$172.64	12.127%	$193.5761	$193.58	$193.60	$193.60
Purchase #6	$34.74	7.780%	$37.4428	$37.44	$37.45	$37.40
Purchase #7	$38.88	6.723%	$41.4939	$41.49	$41.50	$41.50
7 purchase totals =	$921.51		$1,022.8960	$1,022.89	$1,022.90	$1,022.90