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	$135.33	4.831%	$141.8678	$141.87	$141.85	$141.90
Purchase #2	$105.65	3.805%	$109.67	$109.67	$109.65	$109.70
Purchase #3	$8.98	12.294%	$10.084	$10.08	$10.10	$10.10
Purchase #4	$73.86	6.692%	$78.8027	$78.80	$78.80	$78.80
Purchase #5	$200.61	8.360%	$217.381	$217.38	$217.40	$217.40
Purchase #6	$167.25	7.375%	$179.5847	$179.58	$179.60	$179.60
Purchase #7	$195.87	12.874%	$221.0863	$221.09	$221.10	$221.10
7 purchase totals =	$887.55		$958.4765	$958.47	$958.50	$958.60