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	$34.57	7.774%	$37.2575	$37.26	$37.25	$37.30
Purchase #2	$39.68	6.666%	$42.3251	$42.33	$42.35	$42.30
Purchase #3	$28.51	10.605%	$31.5335	$31.53	$31.55	$31.50
Purchase #4	$82.86	11.445%	$92.3433	$92.34	$92.35	$92.30
Purchase #5	$73.69	5.622%	$77.8329	$77.83	$77.85	$77.80
Purchase #6	$31.79	3.109%	$32.7784	$32.78	$32.80	$32.80
Purchase #7	$67.97	13.142%	$76.9026	$76.90	$76.90	$76.90
7 purchase totals =	$359.07		$390.9733	$390.97	$391.05	$390.90