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	$115.46	11.231%	$128.4273	$128.43	$128.45	$128.40
Purchase #2	$146.61	10.683%	$162.2723	$162.27	$162.25	$162.30
Purchase #3	$199.51	13.229%	$225.9032	$225.90	$225.90	$225.90
Purchase #4	$23.74	12.660%	$26.7455	$26.75	$26.75	$26.70
Purchase #5	$38.38	9.357%	$41.9712	$41.97	$41.95	$42.00
Purchase #6	$78.58	6.694%	$83.8401	$83.84	$83.85	$83.80
Purchase #7	$68.82	4.273%	$71.7607	$71.76	$71.75	$71.80
7 purchase totals =	$671.10		$740.9203	$740.92	$740.90	$740.90