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	$221.46	13.547%	$251.4612	$251.46	$251.45	$251.50
Purchase #2	$103.40	10.543%	$114.3015	$114.30	$114.30	$114.30
Purchase #3	$151.27	5.702%	$159.8954	$159.90	$159.90	$159.90
Purchase #4	$130.54	5.839%	$138.1622	$138.16	$138.15	$138.20
Purchase #5	$30.77	8.703%	$33.4479	$33.45	$33.45	$33.40
Purchase #6	$196.98	13.334%	$223.2453	$223.25	$223.25	$223.20
Purchase #7	$89.36	11.367%	$99.5176	$99.52	$99.50	$99.50
7 purchase totals =	$923.78		$1,020.0311	$1,020.04	$1,020.00	$1,020.00