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	$80.35	12.396%	$90.3102	$90.31	$90.30	$90.30
Purchase #2	$45.63	7.476%	$49.0413	$49.04	$49.05	$49.00
Purchase #3	$172.77	9.151%	$188.5802	$188.58	$188.60	$188.60
Purchase #4	$133.56	12.556%	$150.3298	$150.33	$150.35	$150.30
Purchase #5	$115.45	4.347%	$120.4686	$120.47	$120.45	$120.50
Purchase #6	$48.45	12.193%	$54.3575	$54.36	$54.35	$54.40
Purchase #7	$132.34	6.141%	$140.467	$140.47	$140.45	$140.50
7 purchase totals =	$728.55		$793.5546	$793.56	$793.55	$793.60