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	$72.86	7.290%	$78.1715	$78.17	$78.15	$78.20
Purchase #2	$238.61	5.119%	$250.8244	$250.82	$250.80	$250.80
Purchase #3	$28.66	3.431%	$29.6433	$29.64	$29.65	$29.60
Purchase #4	$39.72	3.398%	$41.0697	$41.07	$41.05	$41.10
Purchase #5	$172.73	6.614%	$184.1544	$184.15	$184.15	$184.20
Purchase #6	$158.52	11.868%	$177.3332	$177.33	$177.35	$177.30
Purchase #7	$193.66	12.236%	$217.3562	$217.36	$217.35	$217.40
7 purchase totals =	$904.76		$978.5527	$978.54	$978.50	$978.60