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	$24.74	12.560%	$27.8473	$27.85	$27.85	$27.80
Purchase #2	$175.83	11.654%	$196.3212	$196.32	$196.30	$196.30
Purchase #3	$109.89	10.245%	$121.1482	$121.15	$121.15	$121.10
Purchase #4	$223.59	8.869%	$243.4202	$243.42	$243.40	$243.40
Purchase #5	$129.72	9.760%	$142.3807	$142.38	$142.40	$142.40
Purchase #6	$123.81	4.329%	$129.1697	$129.17	$129.15	$129.20
Purchase #7	$244.89	11.861%	$273.9364	$273.94	$273.95	$273.90
7 purchase totals =	$1,032.47		$1,134.2237	$1,134.23	$1,134.20	$1,134.10