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	$115.78	4.799%	$121.3363	$121.34	$121.35	$121.30
Purchase #2	$68.88	12.591%	$77.5527	$77.55	$77.55	$77.60
Purchase #3	$215.64	13.153%	$244.0031	$244.00	$244.00	$244.00
Purchase #4	$104.85	7.302%	$112.5061	$112.51	$112.50	$112.50
Purchase #5	$79.73	12.226%	$89.4778	$89.48	$89.50	$89.50
Purchase #6	$89.34	6.342%	$95.0059	$95.01	$95.00	$95.00
Purchase #7	$41.74	9.861%	$45.856	$45.86	$45.85	$45.90
7 purchase totals =	$715.96		$785.7379	$785.75	$785.75	$785.80