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	$131.79	4.250%	$137.3911	$137.39	$137.40	$137.40
Purchase #2	$43.44	10.323%	$47.9243	$47.92	$47.90	$47.90
Purchase #3	$210.91	5.318%	$222.1262	$222.13	$222.15	$222.10
Purchase #4	$109.49	5.681%	$115.7101	$115.71	$115.70	$115.70
Purchase #5	$88.51	13.696%	$100.6323	$100.63	$100.65	$100.60
Purchase #6	$16.88	13.591%	$19.1742	$19.17	$19.15	$19.20
Purchase #7	$90.64	11.361%	$100.9376	$100.94	$100.95	$100.90
7 purchase totals =	$691.66		$743.8958	$743.89	$743.90	$743.80