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	$237.42	4.654%	$248.4695	$248.47	$248.45	$248.50
Purchase #2	$18.53	9.111%	$20.2183	$20.22	$20.20	$20.20
Purchase #3	$69.91	5.646%	$73.8571	$73.86	$73.85	$73.90
Purchase #4	$36.73	13.811%	$41.8028	$41.80	$41.80	$41.80
Purchase #5	$146.82	13.249%	$166.2722	$166.27	$166.25	$166.30
Purchase #6	$61.38	13.213%	$69.4901	$69.49	$69.50	$69.50
Purchase #7	$51.31	7.768%	$55.2958	$55.30	$55.30	$55.30
7 purchase totals =	$622.10		$675.4058	$675.41	$675.35	$675.50