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	$133.83	3.316%	$138.2678	$138.27	$138.25	$138.30
Purchase #2	$247.93	10.308%	$273.4866	$273.49	$273.50	$273.50
Purchase #3	$23.46	7.618%	$25.2472	$25.25	$25.25	$25.20
Purchase #4	$148.73	10.454%	$164.2782	$164.28	$164.30	$164.30
Purchase #5	$59.37	3.379%	$61.3761	$61.38	$61.40	$61.40
Purchase #6	$171.98	10.512%	$190.0585	$190.06	$190.05	$190.10
Purchase #7	$126.51	3.308%	$130.695	$130.70	$130.70	$130.70
7 purchase totals =	$911.81		$983.4094	$983.43	$983.45	$983.50