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	$18.48	9.787%	$20.2886	$20.29	$20.30	$20.30
Purchase #2	$231.90	13.856%	$264.0321	$264.03	$264.05	$264.00
Purchase #3	$55.61	3.776%	$57.7098	$57.71	$57.70	$57.70
Purchase #4	$98.25	5.264%	$103.4219	$103.42	$103.40	$103.40
Purchase #5	$92.83	11.264%	$103.2864	$103.29	$103.30	$103.30
Purchase #6	$102.69	10.136%	$113.0987	$113.10	$113.10	$113.10
Purchase #7	$166.96	9.167%	$182.2652	$182.27	$182.25	$182.30
7 purchase totals =	$766.72		$844.1027	$844.11	$844.10	$844.10