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	$51.89	5.752%	$54.8747	$54.87	$54.85	$54.90
Purchase #2	$88.74	8.489%	$96.2731	$96.27	$96.25	$96.30
Purchase #3	$24.69	10.817%	$27.3607	$27.36	$27.35	$27.40
Purchase #4	$56.30	5.247%	$59.2541	$59.25	$59.25	$59.30
Purchase #5	$141.46	7.767%	$152.4472	$152.45	$152.45	$152.40
Purchase #6	$82.37	3.367%	$85.1434	$85.14	$85.15	$85.10
Purchase #7	$153.90	13.459%	$174.6134	$174.61	$174.60	$174.60
7 purchase totals =	$599.35		$649.9666	$649.95	$649.90	$650.00