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	$69.92	11.504%	$77.9636	$77.96	$77.95	$78.00
Purchase #2	$209.85	10.290%	$231.4436	$231.44	$231.45	$231.40
Purchase #3	$233.54	7.710%	$251.5459	$251.55	$251.55	$251.50
Purchase #4	$86.68	10.736%	$95.986	$95.99	$96.00	$96.00
Purchase #5	$105.47	5.680%	$111.4607	$111.46	$111.45	$111.50
Purchase #6	$250.71	3.510%	$259.5099	$259.51	$259.50	$259.50
Purchase #7	$156.25	3.374%	$161.5219	$161.52	$161.50	$161.50
7 purchase totals =	$1,112.42		$1,189.4316	$1,189.43	$1,189.40	$1,189.40