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	$109.70	6.669%	$117.0159	$117.02	$117.00	$117.00
Purchase #2	$52.69	12.559%	$59.3073	$59.31	$59.30	$59.30
Purchase #3	$36.46	13.397%	$41.3445	$41.34	$41.35	$41.30
Purchase #4	$168.27	10.527%	$185.9838	$185.98	$186.00	$186.00
Purchase #5	$192.87	3.833%	$200.2627	$200.26	$200.25	$200.30
Purchase #6	$237.27	13.184%	$268.5517	$268.55	$268.55	$268.60
Purchase #7	$117.53	7.109%	$125.8852	$125.89	$125.90	$125.90
7 purchase totals =	$914.79		$998.3511	$998.35	$998.35	$998.40