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	$59.71	6.133%	$63.372	$63.37	$63.35	$63.40
Purchase #2	$58.48	11.853%	$65.4116	$65.41	$65.40	$65.40
Purchase #3	$40.92	8.598%	$44.4383	$44.44	$44.45	$44.40
Purchase #4	$26.59	8.732%	$28.9118	$28.91	$28.90	$28.90
Purchase #5	$123.59	12.659%	$139.2353	$139.24	$139.25	$139.20
Purchase #6	$162.59	4.508%	$169.9196	$169.92	$169.90	$169.90
Purchase #7	$139.67	13.393%	$158.376	$158.38	$158.40	$158.40
7 purchase totals =	$611.55		$669.6646	$669.67	$669.65	$669.60