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	$35.71	3.731%	$37.0423	$37.04	$37.05	$37.00
Purchase #2	$147.26	13.657%	$167.3713	$167.37	$167.35	$167.40
Purchase #3	$23.39	13.481%	$26.5432	$26.54	$26.55	$26.50
Purchase #4	$27.89	11.622%	$31.1314	$31.13	$31.15	$31.10
Purchase #5	$55.73	12.338%	$62.606	$62.61	$62.60	$62.60
Purchase #6	$217.98	3.370%	$225.3259	$225.33	$225.35	$225.30
Purchase #7	$82.56	10.194%	$90.9762	$90.98	$91.00	$91.00
7 purchase totals =	$590.52		$640.9963	$641.00	$641.05	$640.90