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	$129.43	5.618%	$136.7014	$136.70	$136.70	$136.70
Purchase #2	$38.36	6.590%	$40.8879	$40.89	$40.90	$40.90
Purchase #3	$18.58	10.453%	$20.5222	$20.52	$20.50	$20.50
Purchase #4	$96.91	7.231%	$103.9176	$103.92	$103.90	$103.90
Purchase #5	$6.66	5.404%	$7.0199	$7.02	$7.00	$7.00
Purchase #6	$136.99	5.738%	$144.8505	$144.85	$144.85	$144.90
Purchase #7	$98.40	6.812%	$105.103	$105.10	$105.10	$105.10
7 purchase totals =	$525.33		$559.0025	$559.00	$558.95	$559.00