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	$30.34	13.127%	$34.3227	$34.32	$34.30	$34.30
Purchase #2	$191.76	9.489%	$209.9561	$209.96	$209.95	$210.00
Purchase #3	$164.93	5.768%	$174.4432	$174.44	$174.45	$174.40
Purchase #4	$80.80	9.498%	$88.4744	$88.47	$88.45	$88.50
Purchase #5	$86.63	12.297%	$97.2829	$97.28	$97.30	$97.30
Purchase #6	$38.67	10.128%	$42.5865	$42.59	$42.60	$42.60
Purchase #7	$141.80	6.157%	$150.5306	$150.53	$150.55	$150.50
7 purchase totals =	$734.93		$797.5964	$797.59	$797.60	$797.60