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	$13.85	13.442%	$15.7117	$15.71	$15.70	$15.70
Purchase #2	$136.31	8.516%	$147.9182	$147.92	$147.90	$147.90
Purchase #3	$98.96	5.559%	$104.4612	$104.46	$104.45	$104.50
Purchase #4	$86.59	9.128%	$94.4939	$94.49	$94.50	$94.50
Purchase #5	$212.59	4.533%	$222.2267	$222.23	$222.25	$222.20
Purchase #6	$42.48	12.576%	$47.8223	$47.82	$47.80	$47.80
Purchase #7	$244.30	7.799%	$263.353	$263.35	$263.35	$263.40
7 purchase totals =	$835.08		$895.9870	$895.98	$895.95	$896.00