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	$192.69	3.842%	$200.0931	$200.09	$200.10	$200.10
Purchase #2	$140.66	11.284%	$156.5321	$156.53	$156.55	$156.50
Purchase #3	$116.86	9.860%	$128.3824	$128.38	$128.40	$128.40
Purchase #4	$21.38	9.141%	$23.3343	$23.33	$23.35	$23.30
Purchase #5	$94.72	13.478%	$107.4864	$107.49	$107.50	$107.50
Purchase #6	$124.25	5.534%	$131.126	$131.13	$131.15	$131.10
Purchase #7	$130.98	7.503%	$140.8074	$140.81	$140.80	$140.80
7 purchase totals =	$821.54		$887.7617	$887.76	$887.85	$887.70