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	$197.93	4.389%	$206.6171	$206.62	$206.60	$206.60
Purchase #2	$237.57	12.297%	$266.784	$266.78	$266.80	$266.80
Purchase #3	$31.34	3.501%	$32.4372	$32.44	$32.45	$32.40
Purchase #4	$86.47	13.802%	$98.4046	$98.40	$98.40	$98.40
Purchase #5	$78.90	8.260%	$85.4171	$85.42	$85.40	$85.40
Purchase #6	$243.38	10.638%	$269.2708	$269.27	$269.25	$269.30
Purchase #7	$144.28	4.124%	$150.2301	$150.23	$150.25	$150.20
7 purchase totals =	$1,019.87		$1,109.1609	$1,109.16	$1,109.15	$1,109.10