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	$124.63	3.760%	$129.3161	$129.32	$129.30	$129.30
Purchase #2	$217.56	7.391%	$233.6399	$233.64	$233.65	$233.60
Purchase #3	$133.94	4.711%	$140.2499	$140.25	$140.25	$140.20
Purchase #4	$163.59	13.131%	$185.071	$185.07	$185.05	$185.10
Purchase #5	$229.42	5.650%	$242.3822	$242.38	$242.40	$242.40
Purchase #6	$154.65	6.590%	$164.8414	$164.84	$164.85	$164.80
Purchase #7	$179.61	9.150%	$196.0443	$196.04	$196.05	$196.00
7 purchase totals =	$1,203.40		$1,291.5448	$1,291.54	$1,291.55	$1,291.40