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	$249.90	5.535%	$263.732	$263.73	$263.75	$263.70
Purchase #2	$149.72	10.318%	$165.1681	$165.17	$165.15	$165.20
Purchase #3	$40.33	7.167%	$43.2205	$43.22	$43.20	$43.20
Purchase #4	$229.38	8.402%	$248.6525	$248.65	$248.65	$248.70
Purchase #5	$238.80	13.363%	$270.7108	$270.71	$270.70	$270.70
Purchase #6	$98.97	6.709%	$105.6099	$105.61	$105.60	$105.60
Purchase #7	$20.25	6.358%	$21.5375	$21.54	$21.55	$21.50
7 purchase totals =	$1,027.35		$1,118.6313	$1,118.63	$1,118.60	$1,118.60