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	$154.75	8.467%	$167.8527	$167.85	$167.85	$167.90
Purchase #2	$35.90	11.193%	$39.9183	$39.92	$39.90	$39.90
Purchase #3	$18.69	11.195%	$20.7823	$20.78	$20.80	$20.80
Purchase #4	$22.98	12.645%	$25.8858	$25.89	$25.90	$25.90
Purchase #5	$102.32	10.544%	$113.1086	$113.11	$113.10	$113.10
Purchase #6	$217.68	6.652%	$232.1601	$232.16	$232.15	$232.20
Purchase #7	$65.28	4.318%	$68.0988	$68.10	$68.10	$68.10
7 purchase totals =	$617.60		$667.8066	$667.81	$667.80	$667.90