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	$160.96	11.276%	$179.1098	$179.11	$179.10	$179.10
Purchase #2	$156.60	3.466%	$162.0278	$162.03	$162.05	$162.00
Purchase #3	$80.78	7.315%	$86.6891	$86.69	$86.70	$86.70
Purchase #4	$80.73	11.805%	$90.2602	$90.26	$90.25	$90.30
Purchase #5	$108.96	9.168%	$118.9495	$118.95	$118.95	$118.90
Purchase #6	$92.36	4.311%	$96.3416	$96.34	$96.35	$96.30
Purchase #7	$232.30	7.648%	$250.0663	$250.07	$250.05	$250.10
7 purchase totals =	$912.69		$983.4443	$983.45	$983.45	$983.40