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	$80.59	6.534%	$85.8558	$85.86	$85.85	$85.90
Purchase #2	$81.57	9.315%	$89.1682	$89.17	$89.15	$89.20
Purchase #3	$138.61	10.145%	$152.672	$152.67	$152.65	$152.70
Purchase #4	$34.69	3.459%	$35.8899	$35.89	$35.90	$35.90
Purchase #5	$177.81	12.258%	$199.6059	$199.61	$199.60	$199.60
Purchase #6	$91.39	9.557%	$100.1241	$100.12	$100.10	$100.10
Purchase #7	$187.36	3.352%	$193.6403	$193.64	$193.65	$193.60
7 purchase totals =	$792.02		$856.9562	$856.96	$856.90	$857.00