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	$18.73	11.236%	$20.8345	$20.83	$20.85	$20.80
Purchase #2	$204.69	9.305%	$223.7364	$223.74	$223.75	$223.70
Purchase #3	$64.62	4.775%	$67.7056	$67.71	$67.70	$67.70
Purchase #4	$228.59	5.665%	$241.5396	$241.54	$241.55	$241.50
Purchase #5	$106.47	7.513%	$114.4691	$114.47	$114.45	$114.50
Purchase #6	$156.96	7.252%	$168.3427	$168.34	$168.35	$168.30
Purchase #7	$103.40	4.761%	$108.3229	$108.32	$108.30	$108.30
7 purchase totals =	$883.46		$944.9508	$944.95	$944.95	$944.80