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	$89.80	11.367%	$100.0076	$100.01	$100.00	$100.00
Purchase #2	$89.34	6.248%	$94.922	$94.92	$94.90	$94.90
Purchase #3	$246.98	12.258%	$277.2548	$277.25	$277.25	$277.30
Purchase #4	$228.46	4.468%	$238.6676	$238.67	$238.65	$238.70
Purchase #5	$182.68	7.782%	$196.8962	$196.90	$196.90	$196.90
Purchase #6	$153.39	9.130%	$167.3945	$167.39	$167.40	$167.40
Purchase #7	$50.55	5.368%	$53.2635	$53.26	$53.25	$53.30
7 purchase totals =	$1,041.20		$1,128.4062	$1,128.40	$1,128.35	$1,128.50