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	$127.35	4.810%	$133.4755	$133.48	$133.50	$133.50
Purchase #2	$155.51	8.360%	$168.5106	$168.51	$168.50	$168.50
Purchase #3	$126.47	7.694%	$136.2006	$136.20	$136.20	$136.20
Purchase #4	$44.64	3.431%	$46.1716	$46.17	$46.15	$46.20
Purchase #5	$139.85	9.342%	$152.9148	$152.91	$152.90	$152.90
Purchase #6	$70.63	10.596%	$78.114	$78.11	$78.10	$78.10
Purchase #7	$29.44	7.775%	$31.729	$31.73	$31.75	$31.70
7 purchase totals =	$693.89		$747.1161	$747.11	$747.10	$747.10