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	$222.30	6.741%	$237.2852	$237.29	$237.30	$237.30
Purchase #2	$153.50	4.462%	$160.3492	$160.35	$160.35	$160.30
Purchase #3	$207.31	13.135%	$234.5402	$234.54	$234.55	$234.50
Purchase #4	$148.38	7.687%	$159.786	$159.79	$159.80	$159.80
Purchase #5	$89.32	11.201%	$99.3247	$99.32	$99.30	$99.30
Purchase #6	$69.97	5.651%	$73.924	$73.92	$73.90	$73.90
Purchase #7	$248.56	4.757%	$260.384	$260.38	$260.40	$260.40
7 purchase totals =	$1,139.34		$1,225.5933	$1,225.59	$1,225.60	$1,225.50