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	$39.85	8.144%	$43.0954	$43.10	$43.10	$43.10
Purchase #2	$165.46	9.306%	$180.8577	$180.86	$180.85	$180.90
Purchase #3	$242.97	13.283%	$275.2437	$275.24	$275.25	$275.20
Purchase #4	$96.56	5.700%	$102.0639	$102.06	$102.05	$102.10
Purchase #5	$121.36	10.817%	$134.4875	$134.49	$134.50	$134.50
Purchase #6	$157.73	11.119%	$175.268	$175.27	$175.25	$175.30
Purchase #7	$150.85	9.223%	$164.7629	$164.76	$164.75	$164.80
7 purchase totals =	$974.78		$1,075.7791	$1,075.78	$1,075.75	$1,075.90