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	$249.57	8.398%	$270.5289	$270.53	$270.55	$270.50
Purchase #2	$82.70	4.143%	$86.1263	$86.13	$86.15	$86.10
Purchase #3	$128.57	9.363%	$140.608	$140.61	$140.60	$140.60
Purchase #4	$27.58	4.356%	$28.7814	$28.78	$28.80	$28.80
Purchase #5	$136.91	12.844%	$154.4947	$154.49	$154.50	$154.50
Purchase #6	$177.72	12.330%	$199.6329	$199.63	$199.65	$199.60
Purchase #7	$35.67	4.792%	$37.3793	$37.38	$37.40	$37.40
7 purchase totals =	$838.72		$917.5515	$917.55	$917.65	$917.50