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	$150.36	9.138%	$164.0999	$164.10	$164.10	$164.10
Purchase #2	$69.81	3.188%	$72.0355	$72.04	$72.05	$72.00
Purchase #3	$37.46	7.266%	$40.1818	$40.18	$40.20	$40.20
Purchase #4	$209.72	4.853%	$219.8977	$219.90	$219.90	$219.90
Purchase #5	$93.93	11.259%	$104.5056	$104.51	$104.50	$104.50
Purchase #6	$165.70	10.253%	$182.6892	$182.69	$182.70	$182.70
Purchase #7	$213.74	4.663%	$223.7067	$223.71	$223.70	$223.70
7 purchase totals =	$940.72		$1,007.1164	$1,007.13	$1,007.15	$1,007.10