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	$81.30	11.367%	$90.5414	$90.54	$90.55	$90.50
Purchase #2	$209.28	9.570%	$229.3081	$229.31	$229.30	$229.30
Purchase #3	$176.76	3.187%	$182.3933	$182.39	$182.40	$182.40
Purchase #4	$217.44	10.517%	$240.3082	$240.31	$240.30	$240.30
Purchase #5	$75.55	11.315%	$84.0985	$84.10	$84.10	$84.10
Purchase #6	$148.42	9.776%	$162.9295	$162.93	$162.95	$162.90
Purchase #7	$190.77	8.601%	$207.1781	$207.18	$207.20	$207.20
7 purchase totals =	$1,099.52		$1,196.7571	$1,196.76	$1,196.80	$1,196.70