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	$152.28	10.461%	$168.21	$168.21	$168.20	$168.20
Purchase #2	$164.66	4.772%	$172.5176	$172.52	$172.50	$172.50
Purchase #3	$70.90	8.490%	$76.9194	$76.92	$76.90	$76.90
Purchase #4	$143.27	9.482%	$156.8549	$156.85	$156.85	$156.90
Purchase #5	$52.79	10.266%	$58.2094	$58.21	$58.20	$58.20
Purchase #6	$71.63	12.165%	$80.3438	$80.34	$80.35	$80.30
Purchase #7	$93.36	8.769%	$101.5467	$101.55	$101.55	$101.50
7 purchase totals =	$748.89		$814.6018	$814.60	$814.55	$814.50