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	$159.83	8.289%	$173.0783	$173.08	$173.10	$173.10
Purchase #2	$160.84	4.435%	$167.9733	$167.97	$167.95	$168.00
Purchase #3	$240.73	12.497%	$270.814	$270.81	$270.80	$270.80
Purchase #4	$167.75	4.653%	$175.5554	$175.56	$175.55	$175.60
Purchase #5	$31.49	4.285%	$32.8393	$32.84	$32.85	$32.80
Purchase #6	$171.25	9.128%	$186.8817	$186.88	$186.90	$186.90
Purchase #7	$95.45	10.801%	$105.7596	$105.76	$105.75	$105.80
7 purchase totals =	$1,027.34		$1,112.9016	$1,112.90	$1,112.90	$1,113.00