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	$244.63	13.189%	$276.8943	$276.89	$276.90	$276.90
Purchase #2	$202.60	7.805%	$218.4129	$218.41	$218.40	$218.40
Purchase #3	$39.70	9.867%	$43.6172	$43.62	$43.60	$43.60
Purchase #4	$40.36	5.649%	$42.6399	$42.64	$42.65	$42.60
Purchase #5	$106.85	6.307%	$113.589	$113.59	$113.60	$113.60
Purchase #6	$38.25	3.535%	$39.6021	$39.60	$39.60	$39.60
Purchase #7	$237.36	13.207%	$268.7081	$268.71	$268.70	$268.70
7 purchase totals =	$909.75		$1,003.4635	$1,003.46	$1,003.45	$1,003.40