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	$105.93	5.658%	$111.9235	$111.92	$111.90	$111.90
Purchase #2	$59.41	11.130%	$66.0223	$66.02	$66.00	$66.00
Purchase #3	$57.25	13.820%	$65.162	$65.16	$65.15	$65.20
Purchase #4	$121.72	6.402%	$129.5125	$129.51	$129.50	$129.50
Purchase #5	$37.49	8.107%	$40.5293	$40.53	$40.55	$40.50
Purchase #6	$84.54	11.850%	$94.558	$94.56	$94.55	$94.60
Purchase #7	$29.39	8.492%	$31.8858	$31.89	$31.90	$31.90
7 purchase totals =	$495.73		$539.5934	$539.59	$539.55	$539.60