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	$52.87	9.585%	$57.9376	$57.94	$57.95	$57.90
Purchase #2	$171.31	10.241%	$188.8539	$188.85	$188.85	$188.90
Purchase #3	$187.81	11.410%	$209.2391	$209.24	$209.25	$209.20
Purchase #4	$35.30	4.802%	$36.9951	$37.00	$37.00	$37.00
Purchase #5	$243.63	11.831%	$272.4539	$272.45	$272.45	$272.50
Purchase #6	$116.39	6.422%	$123.8646	$123.86	$123.85	$123.90
Purchase #7	$76.28	13.483%	$86.5648	$86.56	$86.55	$86.60
7 purchase totals =	$883.59		$975.9090	$975.90	$975.90	$976.00