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	$120.79	5.298%	$127.1895	$127.19	$127.20	$127.20
Purchase #2	$250.46	9.512%	$274.2838	$274.28	$274.30	$274.30
Purchase #3	$243.59	10.249%	$268.5555	$268.56	$268.55	$268.60
Purchase #4	$196.85	5.832%	$208.3303	$208.33	$208.35	$208.30
Purchase #5	$83.32	8.314%	$90.2472	$90.25	$90.25	$90.20
Purchase #6	$89.77	3.219%	$92.6597	$92.66	$92.65	$92.70
Purchase #7	$126.77	10.697%	$140.3306	$140.33	$140.35	$140.30
7 purchase totals =	$1,111.55		$1,201.5966	$1,201.60	$1,201.65	$1,201.60