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	$93.34	7.590%	$100.4245	$100.42	$100.40	$100.40
Purchase #2	$38.68	10.705%	$42.8207	$42.82	$42.80	$42.80
Purchase #3	$50.91	11.560%	$56.7952	$56.80	$56.80	$56.80
Purchase #4	$245.96	13.524%	$279.2236	$279.22	$279.20	$279.20
Purchase #5	$11.57	11.253%	$12.872	$12.87	$12.85	$12.90
Purchase #6	$129.86	10.750%	$143.82	$143.82	$143.80	$143.80
Purchase #7	$103.45	6.871%	$110.558	$110.56	$110.55	$110.60
7 purchase totals =	$673.77		$746.5140	$746.51	$746.40	$746.50