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	$27.52	3.104%	$28.3742	$28.37	$28.35	$28.40
Purchase #2	$157.77	8.720%	$171.5275	$171.53	$171.55	$171.50
Purchase #3	$145.84	11.664%	$162.8508	$162.85	$162.85	$162.90
Purchase #4	$65.67	6.404%	$69.8755	$69.88	$69.90	$69.90
Purchase #5	$151.37	13.121%	$171.2313	$171.23	$171.25	$171.20
Purchase #6	$142.79	5.350%	$150.4293	$150.43	$150.45	$150.40
Purchase #7	$107.76	11.408%	$120.0533	$120.05	$120.05	$120.10
7 purchase totals =	$798.72		$874.3419	$874.34	$874.40	$874.40