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	$112.97	5.258%	$118.91	$118.91	$118.90	$118.90
Purchase #2	$30.94	12.457%	$34.7942	$34.79	$34.80	$34.80
Purchase #3	$92.92	6.731%	$99.1744	$99.17	$99.15	$99.20
Purchase #4	$138.55	12.102%	$155.3173	$155.32	$155.30	$155.30
Purchase #5	$38.86	9.758%	$42.652	$42.65	$42.65	$42.70
Purchase #6	$21.69	7.515%	$23.32	$23.32	$23.30	$23.30
Purchase #7	$37.91	3.768%	$39.3384	$39.34	$39.35	$39.30
7 purchase totals =	$473.84		$513.5063	$513.50	$513.45	$513.50