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	$211.94	4.797%	$222.1068	$222.11	$222.10	$222.10
Purchase #2	$116.27	12.671%	$131.0026	$131.00	$131.00	$131.00
Purchase #3	$10.63	3.559%	$11.0083	$11.01	$11.00	$11.00
Purchase #4	$52.89	7.506%	$56.8599	$56.86	$56.85	$56.90
Purchase #5	$207.63	12.329%	$233.2287	$233.23	$233.25	$233.20
Purchase #6	$165.95	3.840%	$172.3225	$172.32	$172.30	$172.30
Purchase #7	$156.87	4.861%	$164.4955	$164.50	$164.50	$164.50
7 purchase totals =	$922.18		$991.0243	$991.03	$991.00	$991.00