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	$232.38	4.769%	$243.4622	$243.46	$243.45	$243.50
Purchase #2	$152.84	12.293%	$171.6286	$171.63	$171.65	$171.60
Purchase #3	$44.37	6.495%	$47.2518	$47.25	$47.25	$47.30
Purchase #4	$40.35	4.669%	$42.2339	$42.23	$42.25	$42.20
Purchase #5	$243.62	5.436%	$256.8632	$256.86	$256.85	$256.90
Purchase #6	$6.27	12.215%	$7.0359	$7.04	$7.05	$7.00
Purchase #7	$101.52	3.814%	$105.392	$105.39	$105.40	$105.40
7 purchase totals =	$821.35		$873.8676	$873.86	$873.90	$873.90