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	$25.38	7.782%	$27.3551	$27.36	$27.35	$27.40
Purchase #2	$28.80	8.784%	$31.3298	$31.33	$31.35	$31.30
Purchase #3	$43.27	4.538%	$45.2336	$45.23	$45.25	$45.20
Purchase #4	$223.97	11.404%	$249.5115	$249.51	$249.50	$249.50
Purchase #5	$165.43	4.823%	$173.4087	$173.41	$173.40	$173.40
Purchase #6	$27.60	4.872%	$28.9447	$28.94	$28.95	$28.90
Purchase #7	$209.76	8.111%	$226.7736	$226.77	$226.75	$226.80
7 purchase totals =	$724.21		$782.5570	$782.55	$782.55	$782.50