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	$49.55	12.395%	$55.6917	$55.69	$55.70	$55.70
Purchase #2	$89.98	13.808%	$102.4044	$102.40	$102.40	$102.40
Purchase #3	$11.92	11.829%	$13.33	$13.33	$13.35	$13.30
Purchase #4	$156.25	11.458%	$174.1531	$174.15	$174.15	$174.20
Purchase #5	$40.74	12.241%	$45.727	$45.73	$45.75	$45.70
Purchase #6	$64.82	9.743%	$71.1354	$71.14	$71.15	$71.10
Purchase #7	$147.78	13.196%	$167.281	$167.28	$167.30	$167.30
7 purchase totals =	$561.04		$629.7226	$629.72	$629.80	$629.70