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	$203.46	12.843%	$229.5904	$229.59	$229.60	$229.60
Purchase #2	$170.77	5.711%	$180.5227	$180.52	$180.50	$180.50
Purchase #3	$90.49	12.346%	$101.6619	$101.66	$101.65	$101.70
Purchase #4	$140.67	11.444%	$156.7683	$156.77	$156.75	$156.80
Purchase #5	$139.59	8.140%	$150.9526	$150.95	$150.95	$151.00
Purchase #6	$30.64	6.249%	$32.5547	$32.55	$32.55	$32.60
Purchase #7	$100.91	8.405%	$109.3915	$109.39	$109.40	$109.40
7 purchase totals =	$876.53		$961.4421	$961.43	$961.40	$961.60