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	$18.73	10.234%	$20.6468	$20.65	$20.65	$20.60
Purchase #2	$143.43	6.585%	$152.8749	$152.87	$152.85	$152.90
Purchase #3	$187.66	4.831%	$196.7259	$196.73	$196.75	$196.70
Purchase #4	$98.90	3.122%	$101.9877	$101.99	$102.00	$102.00
Purchase #5	$236.41	13.840%	$269.1291	$269.13	$269.15	$269.10
Purchase #6	$206.78	7.796%	$222.9006	$222.90	$222.90	$222.90
Purchase #7	$74.65	4.725%	$78.1772	$78.18	$78.20	$78.20
7 purchase totals =	$966.56		$1,042.4422	$1,042.45	$1,042.50	$1,042.40