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	$170.60	5.447%	$179.8926	$179.89	$179.90	$179.90
Purchase #2	$116.38	7.780%	$125.4344	$125.43	$125.45	$125.40
Purchase #3	$55.27	8.292%	$59.853	$59.85	$59.85	$59.90
Purchase #4	$156.28	12.597%	$175.9666	$175.97	$175.95	$176.00
Purchase #5	$249.26	7.267%	$267.3737	$267.37	$267.35	$267.40
Purchase #6	$33.69	8.367%	$36.5088	$36.51	$36.50	$36.50
Purchase #7	$205.25	10.797%	$227.4108	$227.41	$227.40	$227.40
7 purchase totals =	$986.73		$1,072.4399	$1,072.43	$1,072.40	$1,072.50