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	$28.27	12.585%	$31.8278	$31.83	$31.85	$31.80
Purchase #2	$184.55	11.240%	$205.2934	$205.29	$205.30	$205.30
Purchase #3	$125.52	11.563%	$140.0339	$140.03	$140.05	$140.00
Purchase #4	$223.85	8.579%	$243.0541	$243.05	$243.05	$243.10
Purchase #5	$95.98	6.318%	$102.044	$102.04	$102.05	$102.00
Purchase #6	$218.77	4.640%	$228.9209	$228.92	$228.90	$228.90
Purchase #7	$182.65	4.472%	$190.8181	$190.82	$190.80	$190.80
7 purchase totals =	$1,059.59		$1,141.9922	$1,141.98	$1,142.00	$1,141.90