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	$248.30	8.436%	$269.2466	$269.25	$269.25	$269.20
Purchase #2	$154.56	4.108%	$160.9093	$160.91	$160.90	$160.90
Purchase #3	$83.74	8.548%	$90.8981	$90.90	$90.90	$90.90
Purchase #4	$40.27	3.768%	$41.7874	$41.79	$41.80	$41.80
Purchase #5	$16.67	13.561%	$18.9306	$18.93	$18.95	$18.90
Purchase #6	$199.46	4.802%	$209.0381	$209.04	$209.05	$209.00
Purchase #7	$93.36	7.140%	$100.0259	$100.03	$100.05	$100.00
7 purchase totals =	$836.36		$890.8360	$890.85	$890.90	$890.70