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	$136.48	12.348%	$153.3326	$153.33	$153.35	$153.30
Purchase #2	$51.25	3.780%	$53.1873	$53.19	$53.20	$53.20
Purchase #3	$129.25	8.348%	$140.0398	$140.04	$140.05	$140.00
Purchase #4	$37.76	6.211%	$40.1053	$40.11	$40.10	$40.10
Purchase #5	$51.55	8.775%	$56.0735	$56.07	$56.05	$56.10
Purchase #6	$68.57	5.529%	$72.3612	$72.36	$72.35	$72.40
Purchase #7	$40.87	3.826%	$42.4337	$42.43	$42.45	$42.40
7 purchase totals =	$515.73		$557.5334	$557.53	$557.55	$557.50