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	$107.88	11.218%	$119.982	$119.98	$120.00	$120.00
Purchase #2	$82.51	8.529%	$89.5473	$89.55	$89.55	$89.50
Purchase #3	$59.41	10.301%	$65.5298	$65.53	$65.55	$65.50
Purchase #4	$83.45	7.339%	$89.5744	$89.57	$89.55	$89.60
Purchase #5	$179.40	6.419%	$190.9157	$190.92	$190.90	$190.90
Purchase #6	$250.53	6.726%	$267.3806	$267.38	$267.40	$267.40
Purchase #7	$208.32	13.634%	$236.7223	$236.72	$236.70	$236.70
7 purchase totals =	$971.50		$1,059.6521	$1,059.65	$1,059.65	$1,059.60