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	$95.55	8.755%	$103.9154	$103.92	$103.90	$103.90
Purchase #2	$63.88	11.564%	$71.2671	$71.27	$71.25	$71.30
Purchase #3	$90.37	6.240%	$96.0091	$96.01	$96.00	$96.00
Purchase #4	$174.85	5.873%	$185.1189	$185.12	$185.10	$185.10
Purchase #5	$14.77	4.222%	$15.3936	$15.39	$15.40	$15.40
Purchase #6	$222.70	12.543%	$250.6333	$250.63	$250.65	$250.60
Purchase #7	$195.91	11.159%	$217.7716	$217.77	$217.75	$217.80
7 purchase totals =	$858.03		$940.1090	$940.11	$940.05	$940.10