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	$89.79	6.715%	$95.8194	$95.82	$95.80	$95.80
Purchase #2	$62.80	3.767%	$65.1657	$65.17	$65.15	$65.20
Purchase #3	$223.92	6.371%	$238.1859	$238.19	$238.20	$238.20
Purchase #4	$18.83	7.133%	$20.1731	$20.17	$20.15	$20.20
Purchase #5	$16.56	3.364%	$17.1171	$17.12	$17.10	$17.10
Purchase #6	$31.58	7.435%	$33.928	$33.93	$33.95	$33.90
Purchase #7	$106.82	5.172%	$112.3447	$112.34	$112.35	$112.30
7 purchase totals =	$550.30		$582.7339	$582.74	$582.70	$582.70