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	$38.33	11.439%	$42.7146	$42.71	$42.70	$42.70
Purchase #2	$223.89	10.576%	$247.5686	$247.57	$247.55	$247.60
Purchase #3	$67.47	3.545%	$69.8618	$69.86	$69.85	$69.90
Purchase #4	$114.59	6.285%	$121.792	$121.79	$121.80	$121.80
Purchase #5	$72.35	4.728%	$75.7707	$75.77	$75.75	$75.80
Purchase #6	$180.45	10.123%	$198.717	$198.72	$198.70	$198.70
Purchase #7	$95.46	5.296%	$100.5156	$100.52	$100.50	$100.50
7 purchase totals =	$792.54		$856.9403	$856.94	$856.85	$857.00