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	$133.77	12.262%	$150.1729	$150.17	$150.15	$150.20
Purchase #2	$81.30	8.371%	$88.1056	$88.11	$88.10	$88.10
Purchase #3	$20.81	13.577%	$23.6354	$23.64	$23.65	$23.60
Purchase #4	$184.84	6.529%	$196.9082	$196.91	$196.90	$196.90
Purchase #5	$146.71	12.222%	$164.6409	$164.64	$164.65	$164.60
Purchase #6	$76.44	3.116%	$78.8219	$78.82	$78.80	$78.80
Purchase #7	$44.57	6.769%	$47.5869	$47.59	$47.60	$47.60
7 purchase totals =	$688.44		$749.8718	$749.88	$749.85	$749.80