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	$72.83	7.746%	$78.4714	$78.47	$78.45	$78.50
Purchase #2	$74.66	4.633%	$78.119	$78.12	$78.10	$78.10
Purchase #3	$89.67	10.102%	$98.7285	$98.73	$98.75	$98.70
Purchase #4	$24.35	4.460%	$25.436	$25.44	$25.45	$25.40
Purchase #5	$96.65	3.582%	$100.112	$100.11	$100.10	$100.10
Purchase #6	$77.69	11.477%	$86.6065	$86.61	$86.60	$86.60
Purchase #7	$111.30	11.703%	$124.3254	$124.33	$124.35	$124.30
7 purchase totals =	$547.15		$591.7988	$591.81	$591.80	$591.70