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	$121.59	11.749%	$135.8756	$135.88	$135.90	$135.90
Purchase #2	$233.31	13.787%	$265.4764	$265.48	$265.50	$265.50
Purchase #3	$190.64	3.307%	$196.9445	$196.94	$196.95	$196.90
Purchase #4	$89.55	10.828%	$99.2465	$99.25	$99.25	$99.20
Purchase #5	$159.86	8.276%	$173.09	$173.09	$173.10	$173.10
Purchase #6	$200.71	4.131%	$209.0013	$209.00	$209.00	$209.00
Purchase #7	$6.61	6.273%	$7.0246	$7.02	$7.00	$7.00
7 purchase totals =	$1,002.27		$1,086.6589	$1,086.66	$1,086.70	$1,086.60