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	$43.52	7.524%	$46.7944	$46.79	$46.80	$46.80
Purchase #2	$36.83	3.593%	$38.1533	$38.15	$38.15	$38.20
Purchase #3	$127.94	13.709%	$145.4793	$145.48	$145.50	$145.50
Purchase #4	$203.67	5.640%	$215.157	$215.16	$215.15	$215.20
Purchase #5	$131.60	12.390%	$147.9052	$147.91	$147.90	$147.90
Purchase #6	$35.85	6.436%	$38.1573	$38.16	$38.15	$38.20
Purchase #7	$205.56	11.439%	$229.074	$229.07	$229.05	$229.10
7 purchase totals =	$784.97		$860.7205	$860.72	$860.70	$860.90