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	$24.65	6.853%	$26.3393	$26.34	$26.35	$26.30
Purchase #2	$174.48	7.386%	$187.3671	$187.37	$187.35	$187.40
Purchase #3	$96.31	13.713%	$109.517	$109.52	$109.50	$109.50
Purchase #4	$45.72	13.767%	$52.0143	$52.01	$52.00	$52.00
Purchase #5	$39.50	7.550%	$42.4823	$42.48	$42.50	$42.50
Purchase #6	$65.37	8.709%	$71.0631	$71.06	$71.05	$71.10
Purchase #7	$75.82	12.278%	$85.1292	$85.13	$85.15	$85.10
7 purchase totals =	$521.85		$573.9123	$573.91	$573.90	$573.90