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	$123.82	3.308%	$127.916	$127.92	$127.90	$127.90
Purchase #2	$114.85	7.280%	$123.2111	$123.21	$123.20	$123.20
Purchase #3	$176.82	12.633%	$199.1577	$199.16	$199.15	$199.20
Purchase #4	$226.59	12.410%	$254.7098	$254.71	$254.70	$254.70
Purchase #5	$132.64	7.635%	$142.7671	$142.77	$142.75	$142.80
Purchase #6	$69.86	4.711%	$73.1511	$73.15	$73.15	$73.20
Purchase #7	$152.44	11.472%	$169.9279	$169.93	$169.95	$169.90
7 purchase totals =	$997.02		$1,090.8407	$1,090.85	$1,090.80	$1,090.90