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	$6.41	6.388%	$6.8195	$6.82	$6.80	$6.80
Purchase #2	$218.25	3.730%	$226.3907	$226.39	$226.40	$226.40
Purchase #3	$108.67	13.588%	$123.4361	$123.44	$123.45	$123.40
Purchase #4	$207.34	3.104%	$213.7758	$213.78	$213.80	$213.80
Purchase #5	$231.38	11.241%	$257.3894	$257.39	$257.40	$257.40
Purchase #6	$80.33	11.868%	$89.8636	$89.86	$89.85	$89.90
Purchase #7	$88.86	7.209%	$95.2659	$95.27	$95.25	$95.30
7 purchase totals =	$941.24		$1,012.9410	$1,012.95	$1,012.95	$1,013.00