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	$170.96	7.512%	$183.8025	$183.80	$183.80	$183.80
Purchase #2	$58.86	3.787%	$61.089	$61.09	$61.10	$61.10
Purchase #3	$20.98	4.321%	$21.8865	$21.89	$21.90	$21.90
Purchase #4	$62.81	7.651%	$67.6156	$67.62	$67.60	$67.60
Purchase #5	$155.76	6.776%	$166.3143	$166.31	$166.30	$166.30
Purchase #6	$155.90	6.597%	$166.1847	$166.18	$166.20	$166.20
Purchase #7	$84.31	9.818%	$92.5876	$92.59	$92.60	$92.60
7 purchase totals =	$709.58		$759.4802	$759.48	$759.50	$759.50