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	$42.99	12.345%	$48.2971	$48.30	$48.30	$48.30
Purchase #2	$243.94	12.542%	$274.535	$274.54	$274.55	$274.50
Purchase #3	$165.93	11.588%	$185.158	$185.16	$185.15	$185.20
Purchase #4	$243.68	5.251%	$256.4756	$256.48	$256.50	$256.50
Purchase #5	$181.29	13.235%	$205.2837	$205.28	$205.30	$205.30
Purchase #6	$151.33	11.689%	$169.019	$169.02	$169.00	$169.00
Purchase #7	$109.60	7.290%	$117.5898	$117.59	$117.60	$117.60
7 purchase totals =	$1,138.76		$1,256.3582	$1,256.37	$1,256.40	$1,256.40