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	$161.65	10.306%	$178.3096	$178.31	$178.30	$178.30
Purchase #2	$91.38	13.753%	$103.9475	$103.95	$103.95	$103.90
Purchase #3	$68.52	9.321%	$74.9067	$74.91	$74.90	$74.90
Purchase #4	$46.40	4.648%	$48.5567	$48.56	$48.55	$48.60
Purchase #5	$125.28	11.338%	$139.4842	$139.48	$139.50	$139.50
Purchase #6	$44.45	6.242%	$47.2246	$47.22	$47.20	$47.20
Purchase #7	$73.83	6.705%	$78.7803	$78.78	$78.80	$78.80
7 purchase totals =	$611.51		$671.2096	$671.21	$671.20	$671.20