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	$89.78	6.165%	$95.3149	$95.31	$95.30	$95.30
Purchase #2	$134.43	10.437%	$148.4605	$148.46	$148.45	$148.50
Purchase #3	$107.66	8.534%	$116.8477	$116.85	$116.85	$116.80
Purchase #4	$233.35	4.336%	$243.4681	$243.47	$243.45	$243.50
Purchase #5	$248.41	10.133%	$273.5814	$273.58	$273.60	$273.60
Purchase #6	$50.58	3.459%	$52.3296	$52.33	$52.35	$52.30
Purchase #7	$64.70	4.386%	$67.5377	$67.54	$67.55	$67.50
7 purchase totals =	$928.91		$997.5399	$997.54	$997.55	$997.50