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	$98.78	7.288%	$105.9791	$105.98	$106.00	$106.00
Purchase #2	$23.96	4.678%	$25.0808	$25.08	$25.10	$25.10
Purchase #3	$212.60	13.173%	$240.6058	$240.61	$240.60	$240.60
Purchase #4	$10.71	7.579%	$11.5217	$11.52	$11.50	$11.50
Purchase #5	$215.85	6.513%	$229.9083	$229.91	$229.90	$229.90
Purchase #6	$136.88	3.576%	$141.7748	$141.77	$141.75	$141.80
Purchase #7	$52.34	6.715%	$55.8546	$55.85	$55.85	$55.90
7 purchase totals =	$751.12		$810.7251	$810.72	$810.70	$810.80