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	$54.78	6.538%	$58.3615	$58.36	$58.35	$58.40
Purchase #2	$132.88	5.780%	$140.5605	$140.56	$140.55	$140.60
Purchase #3	$97.40	12.464%	$109.5399	$109.54	$109.55	$109.50
Purchase #4	$24.49	4.138%	$25.5034	$25.50	$25.50	$25.50
Purchase #5	$205.71	11.375%	$229.1095	$229.11	$229.10	$229.10
Purchase #6	$115.93	9.681%	$127.1532	$127.15	$127.15	$127.20
Purchase #7	$96.86	3.815%	$100.5552	$100.56	$100.55	$100.60
7 purchase totals =	$728.05		$790.7832	$790.78	$790.75	$790.90