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	$35.38	13.511%	$40.1602	$40.16	$40.15	$40.20
Purchase #2	$148.50	13.155%	$168.0352	$168.04	$168.05	$168.00
Purchase #3	$59.97	8.148%	$64.8564	$64.86	$64.85	$64.90
Purchase #4	$171.37	8.590%	$186.0907	$186.09	$186.10	$186.10
Purchase #5	$16.30	5.196%	$17.1469	$17.15	$17.15	$17.10
Purchase #6	$39.66	5.744%	$41.9381	$41.94	$41.95	$41.90
Purchase #7	$172.93	13.869%	$196.9137	$196.91	$196.90	$196.90
7 purchase totals =	$644.11		$715.1412	$715.15	$715.15	$715.10