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	$68.92	3.350%	$71.2288	$71.23	$71.25	$71.20
Purchase #2	$150.79	7.682%	$162.3737	$162.37	$162.35	$162.40
Purchase #3	$117.82	13.640%	$133.8906	$133.89	$133.90	$133.90
Purchase #4	$215.89	8.739%	$234.7566	$234.76	$234.75	$234.80
Purchase #5	$76.77	7.570%	$82.5815	$82.58	$82.60	$82.60
Purchase #6	$115.52	11.429%	$128.7228	$128.72	$128.70	$128.70
Purchase #7	$96.98	4.700%	$101.5381	$101.54	$101.55	$101.50
7 purchase totals =	$842.69		$915.0921	$915.09	$915.10	$915.10