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	$110.52	11.207%	$122.906	$122.91	$122.90	$122.90
Purchase #2	$73.72	13.699%	$83.8189	$83.82	$83.80	$83.80
Purchase #3	$238.31	12.692%	$268.5563	$268.56	$268.55	$268.60
Purchase #4	$45.47	10.711%	$50.3403	$50.34	$50.35	$50.30
Purchase #5	$88.81	6.164%	$94.2842	$94.28	$94.30	$94.30
Purchase #6	$244.48	6.321%	$259.9336	$259.93	$259.95	$259.90
Purchase #7	$40.91	4.410%	$42.7141	$42.71	$42.70	$42.70
7 purchase totals =	$842.22		$922.5534	$922.55	$922.55	$922.50