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	$11.70	7.179%	$12.5399	$12.54	$12.55	$12.50
Purchase #2	$188.40	12.129%	$211.251	$211.25	$211.25	$211.30
Purchase #3	$16.53	4.676%	$17.3029	$17.30	$17.30	$17.30
Purchase #4	$11.71	12.168%	$13.1349	$13.13	$13.15	$13.10
Purchase #5	$220.42	3.240%	$227.5616	$227.56	$227.55	$227.60
Purchase #6	$250.50	4.403%	$261.5295	$261.53	$261.55	$261.50
Purchase #7	$85.53	6.121%	$90.7653	$90.77	$90.75	$90.80
7 purchase totals =	$784.79		$834.0851	$834.08	$834.10	$834.10