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	$244.86	11.692%	$273.489	$273.49	$273.50	$273.50
Purchase #2	$110.85	6.513%	$118.0697	$118.07	$118.05	$118.10
Purchase #3	$84.83	5.484%	$89.4821	$89.48	$89.50	$89.50
Purchase #4	$32.75	12.459%	$36.8303	$36.83	$36.85	$36.80
Purchase #5	$82.57	12.426%	$92.8301	$92.83	$92.85	$92.80
Purchase #6	$94.50	13.158%	$106.9343	$106.93	$106.95	$106.90
Purchase #7	$203.28	12.699%	$229.0945	$229.09	$229.10	$229.10
7 purchase totals =	$853.64		$946.7300	$946.72	$946.80	$946.70