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	$41.69	13.490%	$47.314	$47.31	$47.30	$47.30
Purchase #2	$250.35	5.562%	$264.2745	$264.27	$264.25	$264.30
Purchase #3	$80.94	11.202%	$90.0069	$90.01	$90.00	$90.00
Purchase #4	$79.30	8.662%	$86.169	$86.17	$86.15	$86.20
Purchase #5	$195.77	10.752%	$216.8192	$216.82	$216.80	$216.80
Purchase #6	$141.56	4.164%	$147.4546	$147.45	$147.45	$147.50
Purchase #7	$137.68	7.310%	$147.7444	$147.74	$147.75	$147.70
7 purchase totals =	$927.29		$999.7826	$999.77	$999.70	$999.80