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	$67.95	7.261%	$72.8838	$72.88	$72.90	$72.90
Purchase #2	$64.93	11.469%	$72.3768	$72.38	$72.40	$72.40
Purchase #3	$131.27	9.835%	$144.1804	$144.18	$144.20	$144.20
Purchase #4	$147.48	11.591%	$164.5744	$164.57	$164.55	$164.60
Purchase #5	$133.48	11.732%	$149.1399	$149.14	$149.15	$149.10
Purchase #6	$65.95	8.769%	$71.7332	$71.73	$71.75	$71.70
Purchase #7	$12.64	7.135%	$13.5419	$13.54	$13.55	$13.50
7 purchase totals =	$623.70		$688.4304	$688.42	$688.50	$688.40