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	$105.67	9.325%	$115.5237	$115.52	$115.50	$115.50
Purchase #2	$188.82	11.120%	$209.8168	$209.82	$209.80	$209.80
Purchase #3	$93.73	10.360%	$103.4404	$103.44	$103.45	$103.40
Purchase #4	$88.31	9.795%	$96.96	$96.96	$96.95	$97.00
Purchase #5	$57.90	11.125%	$64.3414	$64.34	$64.35	$64.30
Purchase #6	$149.38	4.569%	$156.2052	$156.21	$156.20	$156.20
Purchase #7	$242.46	12.334%	$272.365	$272.37	$272.35	$272.40
7 purchase totals =	$926.27		$1,018.6525	$1,018.66	$1,018.60	$1,018.60