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	$102.41	6.697%	$109.2684	$109.27	$109.25	$109.30
Purchase #2	$63.34	12.774%	$71.4311	$71.43	$71.45	$71.40
Purchase #3	$62.86	4.523%	$65.7032	$65.70	$65.70	$65.70
Purchase #4	$75.77	7.331%	$81.3247	$81.32	$81.30	$81.30
Purchase #5	$142.94	11.849%	$159.877	$159.88	$159.90	$159.90
Purchase #6	$13.54	7.251%	$14.5218	$14.52	$14.50	$14.50
Purchase #7	$89.89	5.752%	$95.0605	$95.06	$95.05	$95.10
7 purchase totals =	$550.75		$597.1867	$597.18	$597.15	$597.20