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	$75.58	7.607%	$81.3294	$81.33	$81.35	$81.30
Purchase #2	$233.25	13.692%	$265.1866	$265.19	$265.20	$265.20
Purchase #3	$206.73	10.444%	$228.3209	$228.32	$228.30	$228.30
Purchase #4	$146.51	8.331%	$158.7157	$158.72	$158.70	$158.70
Purchase #5	$106.64	11.453%	$118.8535	$118.85	$118.85	$118.90
Purchase #6	$163.72	11.724%	$182.9145	$182.91	$182.90	$182.90
Purchase #7	$56.93	4.574%	$59.534	$59.53	$59.55	$59.50
7 purchase totals =	$989.36		$1,094.8546	$1,094.85	$1,094.85	$1,094.80