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	$182.57	13.144%	$206.567	$206.57	$206.55	$206.60
Purchase #2	$128.90	6.117%	$136.7848	$136.78	$136.80	$136.80
Purchase #3	$31.97	3.642%	$33.1343	$33.13	$33.15	$33.10
Purchase #4	$93.49	6.785%	$99.8333	$99.83	$99.85	$99.80
Purchase #5	$70.67	13.249%	$80.0331	$80.03	$80.05	$80.00
Purchase #6	$63.45	5.776%	$67.1149	$67.11	$67.10	$67.10
Purchase #7	$20.27	3.342%	$20.9474	$20.95	$20.95	$20.90
7 purchase totals =	$591.32		$644.4148	$644.40	$644.45	$644.30