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	$122.94	6.787%	$131.2839	$131.28	$131.30	$131.30
Purchase #2	$188.39	7.679%	$202.8565	$202.86	$202.85	$202.90
Purchase #3	$167.61	10.510%	$185.2258	$185.23	$185.25	$185.20
Purchase #4	$104.91	9.525%	$114.9027	$114.90	$114.90	$114.90
Purchase #5	$97.56	7.651%	$105.0243	$105.02	$105.00	$105.00
Purchase #6	$233.77	4.740%	$244.8507	$244.85	$244.85	$244.90
Purchase #7	$129.96	9.208%	$141.9267	$141.93	$141.95	$141.90
7 purchase totals =	$1,045.14		$1,126.0706	$1,126.07	$1,126.10	$1,126.10