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	$27.27	5.327%	$28.7227	$28.72	$28.70	$28.70
Purchase #2	$155.52	10.549%	$171.9258	$171.93	$171.95	$171.90
Purchase #3	$171.68	11.538%	$191.4884	$191.49	$191.50	$191.50
Purchase #4	$220.55	6.455%	$234.7865	$234.79	$234.80	$234.80
Purchase #5	$62.69	11.272%	$69.7564	$69.76	$69.75	$69.80
Purchase #6	$37.76	7.520%	$40.5996	$40.60	$40.60	$40.60
Purchase #7	$38.27	8.725%	$41.6091	$41.61	$41.60	$41.60
7 purchase totals =	$713.74		$778.8885	$778.90	$778.90	$778.90