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	$131.41	12.866%	$148.3172	$148.32	$148.30	$148.30
Purchase #2	$63.51	3.746%	$65.8891	$65.89	$65.90	$65.90
Purchase #3	$185.34	7.337%	$198.9384	$198.94	$198.95	$198.90
Purchase #4	$81.70	7.443%	$87.7809	$87.78	$87.80	$87.80
Purchase #5	$34.53	11.148%	$38.3794	$38.38	$38.40	$38.40
Purchase #6	$53.53	3.834%	$55.5823	$55.58	$55.60	$55.60
Purchase #7	$201.57	9.152%	$220.0177	$220.02	$220.00	$220.00
7 purchase totals =	$751.59		$814.9050	$814.91	$814.95	$814.90