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	$73.90	7.547%	$79.4772	$79.48	$79.50	$79.50
Purchase #2	$78.34	6.798%	$83.6656	$83.67	$83.65	$83.70
Purchase #3	$29.56	12.470%	$33.2461	$33.25	$33.25	$33.20
Purchase #4	$153.61	13.486%	$174.3258	$174.33	$174.35	$174.30
Purchase #5	$164.73	10.418%	$181.8916	$181.89	$181.90	$181.90
Purchase #6	$139.75	3.176%	$144.1885	$144.19	$144.20	$144.20
Purchase #7	$208.65	7.584%	$224.474	$224.47	$224.45	$224.50
7 purchase totals =	$848.54		$921.2688	$921.28	$921.30	$921.30