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	$144.33	8.165%	$156.1145	$156.11	$156.10	$156.10
Purchase #2	$211.97	5.600%	$223.8403	$223.84	$223.85	$223.80
Purchase #3	$163.71	7.418%	$175.854	$175.85	$175.85	$175.90
Purchase #4	$142.78	11.582%	$159.3168	$159.32	$159.30	$159.30
Purchase #5	$123.90	12.141%	$138.9427	$138.94	$138.95	$138.90
Purchase #6	$164.95	12.120%	$184.9419	$184.94	$184.95	$184.90
Purchase #7	$26.61	3.306%	$27.4897	$27.49	$27.50	$27.50
7 purchase totals =	$978.25		$1,066.4999	$1,066.49	$1,066.50	$1,066.40