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	$114.37	12.410%	$128.5633	$128.56	$128.55	$128.60
Purchase #2	$37.49	11.204%	$41.6904	$41.69	$41.70	$41.70
Purchase #3	$167.92	11.858%	$187.832	$187.83	$187.85	$187.80
Purchase #4	$221.39	12.828%	$249.7899	$249.79	$249.80	$249.80
Purchase #5	$48.43	10.146%	$53.3437	$53.34	$53.35	$53.30
Purchase #6	$167.43	3.209%	$172.8028	$172.80	$172.80	$172.80
Purchase #7	$162.33	4.560%	$169.7322	$169.73	$169.75	$169.70
7 purchase totals =	$919.36		$1,003.7543	$1,003.74	$1,003.80	$1,003.70