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	$28.42	3.854%	$29.5153	$29.52	$29.50	$29.50
Purchase #2	$250.36	6.792%	$267.3645	$267.36	$267.35	$267.40
Purchase #3	$59.85	12.787%	$67.503	$67.50	$67.50	$67.50
Purchase #4	$196.37	3.803%	$203.838	$203.84	$203.85	$203.80
Purchase #5	$243.35	10.789%	$269.605	$269.61	$269.60	$269.60
Purchase #6	$189.86	12.491%	$213.5754	$213.58	$213.60	$213.60
Purchase #7	$144.56	5.573%	$152.6163	$152.62	$152.60	$152.60
7 purchase totals =	$1,112.77		$1,204.0175	$1,204.03	$1,204.00	$1,204.00