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	$240.85	13.576%	$273.5478	$273.55	$273.55	$273.50
Purchase #2	$158.76	4.766%	$166.3265	$166.33	$166.35	$166.30
Purchase #3	$35.94	11.387%	$40.0325	$40.03	$40.05	$40.00
Purchase #4	$43.78	12.166%	$49.1063	$49.11	$49.10	$49.10
Purchase #5	$180.74	7.575%	$194.4311	$194.43	$194.45	$194.40
Purchase #6	$30.90	9.610%	$33.8695	$33.87	$33.85	$33.90
Purchase #7	$150.96	12.271%	$169.4843	$169.48	$169.50	$169.50
7 purchase totals =	$841.93		$926.7980	$926.80	$926.85	$926.70