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	$116.97	12.674%	$131.7948	$131.79	$131.80	$131.80
Purchase #2	$77.54	4.736%	$81.2123	$81.21	$81.20	$81.20
Purchase #3	$30.60	3.123%	$31.5556	$31.56	$31.55	$31.60
Purchase #4	$38.48	10.449%	$42.5008	$42.50	$42.50	$42.50
Purchase #5	$125.74	5.570%	$132.7437	$132.74	$132.75	$132.70
Purchase #6	$17.90	12.614%	$20.1579	$20.16	$20.15	$20.20
Purchase #7	$185.89	5.682%	$196.4523	$196.45	$196.45	$196.50
7 purchase totals =	$593.12		$636.4174	$636.41	$636.40	$636.50