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	$249.73	7.141%	$267.5632	$267.56	$267.55	$267.60
Purchase #2	$104.97	8.801%	$114.2084	$114.21	$114.20	$114.20
Purchase #3	$51.89	4.226%	$54.0829	$54.08	$54.10	$54.10
Purchase #4	$32.76	10.191%	$36.0986	$36.10	$36.10	$36.10
Purchase #5	$89.66	7.743%	$96.6024	$96.60	$96.60	$96.60
Purchase #6	$178.97	13.755%	$203.5873	$203.59	$203.60	$203.60
Purchase #7	$59.72	12.731%	$67.323	$67.32	$67.30	$67.30
7 purchase totals =	$767.70		$839.4658	$839.46	$839.45	$839.50