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	$17.83	5.294%	$18.7739	$18.77	$18.75	$18.80
Purchase #2	$85.27	4.820%	$89.38	$89.38	$89.40	$89.40
Purchase #3	$126.82	12.512%	$142.6877	$142.69	$142.70	$142.70
Purchase #4	$227.90	6.348%	$242.3671	$242.37	$242.35	$242.40
Purchase #5	$57.76	3.529%	$59.7984	$59.80	$59.80	$59.80
Purchase #6	$110.40	6.865%	$117.979	$117.98	$118.00	$118.00
Purchase #7	$38.63	8.557%	$41.9356	$41.94	$41.95	$41.90
7 purchase totals =	$664.61		$712.9217	$712.93	$712.95	$713.00