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	$84.74	13.681%	$96.3333	$96.33	$96.35	$96.30
Purchase #2	$209.53	10.649%	$231.8428	$231.84	$231.85	$231.80
Purchase #3	$73.86	11.421%	$82.2956	$82.30	$82.30	$82.30
Purchase #4	$38.82	7.582%	$41.7633	$41.76	$41.75	$41.80
Purchase #5	$179.45	13.174%	$203.0907	$203.09	$203.10	$203.10
Purchase #6	$146.94	3.307%	$151.7993	$151.80	$151.80	$151.80
Purchase #7	$118.54	12.497%	$133.3539	$133.35	$133.35	$133.40
7 purchase totals =	$851.88		$940.4789	$940.47	$940.50	$940.50