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	$81.91	12.788%	$92.3847	$92.38	$92.40	$92.40
Purchase #2	$98.35	5.604%	$103.8615	$103.86	$103.85	$103.90
Purchase #3	$124.84	12.673%	$140.661	$140.66	$140.65	$140.70
Purchase #4	$18.71	7.576%	$20.1275	$20.13	$20.15	$20.10
Purchase #5	$26.54	13.605%	$30.1508	$30.15	$30.15	$30.20
Purchase #6	$145.31	4.529%	$151.8911	$151.89	$151.90	$151.90
Purchase #7	$75.65	13.328%	$85.7326	$85.73	$85.75	$85.70
7 purchase totals =	$571.31		$624.8092	$624.80	$624.85	$624.90