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	$242.95	12.709%	$273.8265	$273.83	$273.85	$273.80
Purchase #2	$40.46	3.270%	$41.783	$41.78	$41.80	$41.80
Purchase #3	$59.37	7.257%	$63.6785	$63.68	$63.70	$63.70
Purchase #4	$84.54	5.848%	$89.4839	$89.48	$89.50	$89.50
Purchase #5	$203.70	9.429%	$222.9069	$222.91	$222.90	$222.90
Purchase #6	$94.42	6.873%	$100.9095	$100.91	$100.90	$100.90
Purchase #7	$102.51	11.205%	$113.9962	$114.00	$114.00	$114.00
7 purchase totals =	$827.95		$906.5845	$906.59	$906.65	$906.60