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	$85.80	3.632%	$88.9163	$88.92	$88.90	$88.90
Purchase #2	$69.28	4.645%	$72.4981	$72.50	$72.50	$72.50
Purchase #3	$100.54	8.614%	$109.2005	$109.20	$109.20	$109.20
Purchase #4	$41.49	6.144%	$44.0391	$44.04	$44.05	$44.00
Purchase #5	$171.46	11.298%	$190.8316	$190.83	$190.85	$190.80
Purchase #6	$110.58	4.800%	$115.8878	$115.89	$115.90	$115.90
Purchase #7	$104.46	11.128%	$116.0843	$116.08	$116.10	$116.10
7 purchase totals =	$683.61		$737.4577	$737.46	$737.50	$737.40