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	$132.83	10.432%	$146.6868	$146.69	$146.70	$146.70
Purchase #2	$82.63	8.873%	$89.9618	$89.96	$89.95	$90.00
Purchase #3	$124.97	11.611%	$139.4803	$139.48	$139.50	$139.50
Purchase #4	$18.89	12.872%	$21.3215	$21.32	$21.30	$21.30
Purchase #5	$85.83	4.754%	$89.9104	$89.91	$89.90	$89.90
Purchase #6	$192.74	9.398%	$210.8537	$210.85	$210.85	$210.90
Purchase #7	$233.80	11.197%	$259.9786	$259.98	$260.00	$260.00
7 purchase totals =	$871.69		$958.1931	$958.19	$958.20	$958.30