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	$159.28	3.457%	$164.7863	$164.79	$164.80	$164.80
Purchase #2	$31.68	9.310%	$34.6294	$34.63	$34.65	$34.60
Purchase #3	$139.34	4.619%	$145.7761	$145.78	$145.80	$145.80
Purchase #4	$54.79	5.804%	$57.97	$57.97	$57.95	$58.00
Purchase #5	$223.95	3.546%	$231.8913	$231.89	$231.90	$231.90
Purchase #6	$247.86	9.380%	$271.1093	$271.11	$271.10	$271.10
Purchase #7	$180.49	9.112%	$196.9362	$196.94	$196.95	$196.90
7 purchase totals =	$1,037.39		$1,103.0986	$1,103.11	$1,103.15	$1,103.10