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	$154.65	8.615%	$167.9731	$167.97	$167.95	$168.00
Purchase #2	$70.93	10.697%	$78.5174	$78.52	$78.50	$78.50
Purchase #3	$211.90	12.523%	$238.4362	$238.44	$238.45	$238.40
Purchase #4	$91.86	10.790%	$101.7717	$101.77	$101.75	$101.80
Purchase #5	$71.82	11.753%	$80.261	$80.26	$80.25	$80.30
Purchase #6	$229.80	8.163%	$248.5586	$248.56	$248.55	$248.60
Purchase #7	$243.31	10.288%	$268.3417	$268.34	$268.35	$268.30
7 purchase totals =	$1,074.27		$1,183.8597	$1,183.86	$1,183.80	$1,183.90