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	$14.61	6.690%	$15.5874	$15.59	$15.60	$15.60
Purchase #2	$90.64	3.506%	$93.8178	$93.82	$93.80	$93.80
Purchase #3	$150.49	6.426%	$160.1605	$160.16	$160.15	$160.20
Purchase #4	$28.55	11.686%	$31.8864	$31.89	$31.90	$31.90
Purchase #5	$167.50	3.432%	$173.2486	$173.25	$173.25	$173.20
Purchase #6	$52.76	8.760%	$57.3818	$57.38	$57.40	$57.40
Purchase #7	$110.71	7.334%	$118.8295	$118.83	$118.85	$118.80
7 purchase totals =	$615.26		$650.9120	$650.92	$650.95	$650.90