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	$94.57	8.421%	$102.5337	$102.53	$102.55	$102.50
Purchase #2	$85.90	12.138%	$96.3265	$96.33	$96.35	$96.30
Purchase #3	$32.78	11.233%	$36.4622	$36.46	$36.45	$36.50
Purchase #4	$79.42	4.341%	$82.8676	$82.87	$82.85	$82.90
Purchase #5	$66.31	8.317%	$71.825	$71.83	$71.85	$71.80
Purchase #6	$113.59	3.569%	$117.644	$117.64	$117.65	$117.60
Purchase #7	$69.48	11.135%	$77.2166	$77.22	$77.20	$77.20
7 purchase totals =	$542.05		$584.8756	$584.88	$584.90	$584.80