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	$248.59	10.596%	$274.9306	$274.93	$274.95	$274.90
Purchase #2	$40.55	12.156%	$45.4793	$45.48	$45.50	$45.50
Purchase #3	$94.31	9.237%	$103.0214	$103.02	$103.00	$103.00
Purchase #4	$228.62	13.219%	$258.8413	$258.84	$258.85	$258.80
Purchase #5	$25.56	8.809%	$27.8116	$27.81	$27.80	$27.80
Purchase #6	$60.33	7.651%	$64.9458	$64.95	$64.95	$64.90
Purchase #7	$189.45	7.472%	$203.6057	$203.61	$203.60	$203.60
7 purchase totals =	$887.41		$978.6357	$978.64	$978.65	$978.50