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	$55.60	6.764%	$59.3608	$59.36	$59.35	$59.40
Purchase #2	$90.32	8.272%	$97.7913	$97.79	$97.80	$97.80
Purchase #3	$212.33	6.238%	$225.5751	$225.58	$225.60	$225.60
Purchase #4	$184.63	6.637%	$196.8839	$196.88	$196.90	$196.90
Purchase #5	$244.98	3.836%	$254.3774	$254.38	$254.40	$254.40
Purchase #6	$132.54	4.475%	$138.4712	$138.47	$138.45	$138.50
Purchase #7	$50.97	5.746%	$53.8987	$53.90	$53.90	$53.90
7 purchase totals =	$971.37		$1,026.3584	$1,026.36	$1,026.40	$1,026.50