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	$35.27	5.580%	$37.2381	$37.24	$37.25	$37.20
Purchase #2	$216.51	7.835%	$233.4736	$233.47	$233.45	$233.50
Purchase #3	$198.79	6.857%	$212.421	$212.42	$212.40	$212.40
Purchase #4	$225.59	4.122%	$234.8888	$234.89	$234.90	$234.90
Purchase #5	$93.60	7.166%	$100.3074	$100.31	$100.30	$100.30
Purchase #6	$70.58	9.768%	$77.4743	$77.47	$77.45	$77.50
Purchase #7	$245.41	11.842%	$274.4715	$274.47	$274.45	$274.50
7 purchase totals =	$1,085.75		$1,170.2747	$1,170.27	$1,170.20	$1,170.30