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	$102.67	4.674%	$107.4688	$107.47	$107.45	$107.50
Purchase #2	$35.78	12.503%	$40.2536	$40.25	$40.25	$40.30
Purchase #3	$96.61	13.588%	$109.7374	$109.74	$109.75	$109.70
Purchase #4	$71.98	13.660%	$81.8125	$81.81	$81.80	$81.80
Purchase #5	$35.63	4.213%	$37.1311	$37.13	$37.15	$37.10
Purchase #6	$125.46	10.428%	$138.543	$138.54	$138.55	$138.50
Purchase #7	$37.59	5.162%	$39.5304	$39.53	$39.55	$39.50
7 purchase totals =	$505.72		$554.4768	$554.47	$554.50	$554.40