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	$72.28	10.113%	$79.5897	$79.59	$79.60	$79.60
Purchase #2	$112.53	10.369%	$124.1982	$124.20	$124.20	$124.20
Purchase #3	$73.27	7.747%	$78.9462	$78.95	$78.95	$78.90
Purchase #4	$81.31	10.524%	$89.8671	$89.87	$89.85	$89.90
Purchase #5	$140.79	4.848%	$147.6155	$147.62	$147.60	$147.60
Purchase #6	$127.63	11.706%	$142.5704	$142.57	$142.55	$142.60
Purchase #7	$104.39	11.303%	$116.1892	$116.19	$116.20	$116.20
7 purchase totals =	$712.20		$778.9763	$778.99	$778.95	$779.00