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	$70.56	9.132%	$77.0035	$77.00	$77.00	$77.00
Purchase #2	$77.56	3.586%	$80.3413	$80.34	$80.35	$80.30
Purchase #3	$38.31	13.245%	$43.3842	$43.38	$43.40	$43.40
Purchase #4	$22.57	6.581%	$24.0553	$24.06	$24.05	$24.10
Purchase #5	$90.35	5.273%	$95.1142	$95.11	$95.10	$95.10
Purchase #6	$161.32	13.802%	$183.5854	$183.59	$183.60	$183.60
Purchase #7	$129.86	13.424%	$147.2924	$147.29	$147.30	$147.30
7 purchase totals =	$590.53		$650.7763	$650.77	$650.80	$650.80