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	$29.89	3.665%	$30.9855	$30.99	$31.00	$31.00
Purchase #2	$90.73	10.870%	$100.5924	$100.59	$100.60	$100.60
Purchase #3	$239.95	12.686%	$270.3901	$270.39	$270.40	$270.40
Purchase #4	$226.80	6.847%	$242.329	$242.33	$242.35	$242.30
Purchase #5	$84.38	6.444%	$89.8174	$89.82	$89.80	$89.80
Purchase #6	$7.87	13.425%	$8.9265	$8.93	$8.95	$8.90
Purchase #7	$239.59	12.369%	$269.2249	$269.22	$269.20	$269.20
7 purchase totals =	$919.21		$1,012.2658	$1,012.27	$1,012.30	$1,012.20