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	$61.61	6.343%	$65.5179	$65.52	$65.50	$65.50
Purchase #2	$232.64	5.697%	$245.8935	$245.89	$245.90	$245.90
Purchase #3	$80.41	10.724%	$89.0332	$89.03	$89.05	$89.00
Purchase #4	$7.50	6.707%	$8.003	$8.00	$8.00	$8.00
Purchase #5	$63.82	4.234%	$66.5221	$66.52	$66.50	$66.50
Purchase #6	$136.44	7.827%	$147.1192	$147.12	$147.10	$147.10
Purchase #7	$68.26	4.176%	$71.1105	$71.11	$71.10	$71.10
7 purchase totals =	$650.68		$693.1994	$693.19	$693.15	$693.10