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	$235.54	12.313%	$264.542	$264.54	$264.55	$264.50
Purchase #2	$234.45	3.313%	$242.2173	$242.22	$242.20	$242.20
Purchase #3	$240.78	5.127%	$253.1248	$253.12	$253.10	$253.10
Purchase #4	$205.37	7.874%	$221.5408	$221.54	$221.55	$221.50
Purchase #5	$131.31	12.561%	$147.8038	$147.80	$147.80	$147.80
Purchase #6	$205.93	9.702%	$225.9093	$225.91	$225.90	$225.90
Purchase #7	$73.68	6.450%	$78.4324	$78.43	$78.45	$78.40
7 purchase totals =	$1,327.06		$1,433.5704	$1,433.56	$1,433.55	$1,433.40