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	$55.41	10.512%	$61.2347	$61.23	$61.25	$61.20
Purchase #2	$127.38	12.199%	$142.9191	$142.92	$142.90	$142.90
Purchase #3	$98.57	3.673%	$102.1905	$102.19	$102.20	$102.20
Purchase #4	$76.89	11.624%	$85.8277	$85.83	$85.85	$85.80
Purchase #5	$6.56	7.385%	$7.0445	$7.04	$7.05	$7.00
Purchase #6	$85.73	13.157%	$97.0095	$97.01	$97.00	$97.00
Purchase #7	$68.43	10.148%	$75.3743	$75.37	$75.35	$75.40
7 purchase totals =	$518.97		$571.6003	$571.59	$571.60	$571.50